Joshua and Margaret
Joshua and Margaret are the parents of Jake and Jermaine, and the adoptive parents of Finn. Finn loves his foster parents very much and treasures Margaret's music box, as seen in "Jake vs. Me-Mow" that she used for lullabies and carries it with him in his backpack; he sees himself as their son and fellow 'puppy.' Finn also states that Margaret raised him to be "graceful" in "Jake Suit."
As housemates, (adoptive) brothers and best friends, Finn and Jake share an incredibly strong bond. Having been raised together by Jake's parents, the duo share a relationship similar to that of siblings, with Jake acting as Finn's older brother. One unique part of Finn's relationship with Jake is Jake's ability to tell when Finn is about to cry, as seen in the episode "Freak City" where it is stated to be a "mother-daughter thing."
Though they have an unconditional love for each other, Finn can get frustrated with Jake because of his laziness and lack of motivation, as seen in many episodes like "The Witch's Garden." As a more laid-back character, Jake often tries to relax Finn's fiery personality in the face of a struggle, frequently advising him not to worry. While he sometimes leads Finn down the wrong path, Jake genuinely means well for his companion and is usually an encouraging and protective figure in Finn's life. In "Incendium," Jake ventures out to find a girlfriend for Finn to fall in love with, and states that he desires for Finn to have "a healthy relationship with someone cool" in "Flute Spell". Finn and Jake have saved each other's lives on several occasions, and often adventure throughout the Land of Ooo together.
In "Dungeon," they both try to survive throughout the dungeon trials; however, they both fail at it and they realise that they need each other as a team to overcome the challenges. This is also evidenced in "Who Would Win," in which Finn says he wants to have an award with Jake, instead of only himself.
However, there are some occasions in which Finn and Jake fight each other. In "Video Makers," they argue on what genre their movie should be, and they refuse to talk to each other until BMO fixes the problem. In the end of every bout or argument, they always reconcile, however. In "Who Would Win," Finn and Jake actually fight each other physically, after Jake won't take training seriously and the ensuing fight caused multiple injuries to both of them. But, in the end of the episode, they go back to being friends again after their confrontation with the Dream Warrior.
In the episode "What Have You Done?", when Finn is seemingly hurt by the fact that Ice King could so easily drop his lifeless body, Jake consoles Finn by saying that if he came across Finn's lifeless body, he would clasp Finn dramatically for a "kajillion" years.
In the episode "Shh!", when Finn and Jake compete to keep silent the whole day, only communicating with written signs, Finn was not able to carry out a normal conversation with the signs he had written. It is then revealed that most of Finn's signs were addressed to Jake and only Jake, including "Hi, Jake", "Thanks, Jake", "That's Funny, Jake", "Nice Catch, Jake", Go Get'm Jake!" and "You The Man, Jake!". Their close friendly and brotherly relationship is also displayed when Finn shows the sign "I Love You, Jake" when he was angry at Jake, and shows the sign "Jake Rules!" when he wanted to cheer Jake up.
In the episode "Dungeon Train", Jake shows genuine love and care for Finn, going as far as to promise to stay on the train with Finn, despite this being against Jake's wishes. Finn also shows his strong bond with Jake, when he was finally able to give up the temptation of staying on the train forever, this willpower arguably fuelled by his love for his brother, when he saw through the future crystal that Jake had stayed on the train with him. Jake was also shown to be truly happy when he found out Finn was going to be alright in the future.
Conversely, in the episode "Dentist" it is revealed from Tiffany that Jake had the skills and prowess to lead a successful life of crime as a 'Criminal Juggernaut', was it not for Finn's influence as Jake's younger brother and best friend, who tore Jake away from Tiffany and their life of crime. Similar to how Finn's love for Jake saved Finn from the Dungeon Train, it is also possible that Jake's love for Finn saved Jake from a life of crime. Furthermore in the same episode, Tiffany said that killing Finn would devastate Jake, a show of their strong bond as brothers and best friends.
In "The New Frontier", Jake was willing to die because he had a "croak dream." This really made Finn uncomfortable, but Jake thought very spiritually about the situation, saying he'll be in his head. But this really upset Finn, not wanting to lose his brother.
In the episode "Ghost Fly", Jake was willing to let BMO momentarily kill him so that he could save Finn from the Ghost Fly's possession. At the end of the episode, when Jake's life was saved by defibrillation, Finn is seen to be extremely relieved and crying as well, demanding Jake never leave him again.
In "Slime Central", after losing a skating contest, Finn, Jake, and Lumpy Space Princess, were forced to be absorbed into Slime Princess' elemental body. Jake was intended to pull them out with his powers but got very comfortable in the slime and faded into it. This really freaked out Finn. Finn was willing to become one with the slime due to losing his brother not knowing if he'd ever see him again, and knowing that Ooo may remain under the elemental spell forever. However LSP managed to get Finn and her out of the slime. After Finn became motivated to save Ooo even more with the idea of saving Jake.In "Skyhooks II", due to Lumpy Space Princess' antielemental "lumps", freeing Ooo from the elemental spell, and turning everything into its "true shape", Jake became a giant, blue-skinned, five-eyed "monster" similar to his shape-shifter parent (who he did not yet know about). Finn was a little creeped out and shocked by his appearance but grew more accepting of it and said that they can fix it. However in "Abstract" Finn was not very accepting and was uncomfortable with his brother's appearance. This upset Jake a lot however he was quickly turned back into his smaller, two-eyed, yellow self again, and everything was okay.
Jake and Lady's puppies
Finn is happy to meet his nieces and nephews in "Jake the Dad" and even wore a shirt which had written upon it "BEST UNKLE" upside down. During the short period of time Finn was with the puppies, he started to play with them (such as when Jake saw him with them he said they're having some "uncle wrestling").
Finn is shown to display a liking to Jake Jr. He also tries to cheer her up in "Another Five More Short Graybles" by joining Jake in a skit to make a time machine to console Jake Jr. about her concerns of the future, even going as far as pretending to be a girl, which he refused to do in "Slow Love."
In future episodes Finn is not shown having much of a relationship with Jake's other children. He rarely interacts with them, and when he does it is extremely awkward. This is shown in "Ocarina", "Wheels", and "The First Investigation", when he interacts with Kim Kil Whan. None of the pups really refer to him as their uncle, possibly due to some of them acting more mature than Finn due to their early adulthood.
In Goliad, Finn and Jake were saved from Goliad by Stormo. Finn soon learned from Bubblegum that Stormo was created from his DNA which caused Finn to realized that Stormo was his son, to which Bubblegum confirmed it like that in a way. Looking at Stormo who was locked an eternal stalemate with Goliad, Finn wished his "son" happy birthday.
MartinBefore the events of the series , when Finn was an infant, Martin was a loving father to Finn. This is shown in the flashbacks in "Min and Marty." Martin enjoyed spending time with his newborn son, and became a better person because of him, and his partner/girlfriend, Minerva Campbell, Finn's mother. However Martin had a past record of coning people, due to this (while Minerva was at work) the home was trespassed by a old foe of Martin, the Widow and her bodyguards. After this Martin ran off with Finn. He went onto a raft and took into the ocean. Martin intended for the two to be safe but the island, Guardian was about to kill the two. Martin decided to sacrifice himself with hopes that Finn would live. Finn however had no way of remembering any of this due to being only a newborn baby.
In "Billy's Bucket List," it is revealed that Finn's human dad is still alive and is stuck at the Citadel (also known as the Crystal Citadel as mentioned in past episodes). At first Finn is shocked that his human dad is alive, but he is nonetheless excited to reunite with him.
Finn finally meets his father in "Escape from the Citadel." Martin acts like a jerk when meeting his son and doesn't even seem to care that he has a son. When Jake tells Martin that Finn's his son he completely ignores Jake and exclaims, "Whaaaat? No starskipper?" in response to Finn telling him they didn't have a starskipper. And when Jake repeats himself, he responds by saying, "Son? Oh. Hey, good for you kid."
Martin does not care for Finn as much as Finn cares for him. He can't even bother to remember his name, calling him "Flynn" once. When Finn asks him why he left him in the woods when he was a baby, he gave a lousy excuse like, "You know me, I'm a funny guy. It was a long time ago. Who knows, maybe you left me!" Martin only acknowledges Finn as his son when he wants something, then leaves him as soon as he gets it. Like when his leg was zapped off, he encouraged Finn to retrieve the Guardian Blood and apply it to his leg, calling him "son" and other things, then as soon as it healed, he swam away shouting, "I got to run to the store!"
In "The Tower", Finn wants revenge on Martin, even going to the extent of building a tower to outer space to rip off Martin's favorite arm. After Princess Bubblegum tricks Finn, he realizes he doesn't want his dad's arm anymore, and feels "neutral."
After crash landing on earth in "Astral Plane" which continued into "The Visitor". Martin came up on a tribe of Villagers. Finn sleepwalked for two days to the village. After two days, he needed water. He drank water from the village until he heard the "tree spirit" which turned out to be Martin. Martin did not want Finn to see him. Martin was actually calling Finn his son many times throughout the episode. Finn was still bothered by him because he was mistreating the villagers. Martin, however, only acted like this towards Finn so he would help him fix the escape pod. After finding out Martin was just leaving the villagers to die, Finn became furious and sent Martin back to space, even after Martin offered to take Finn with him into space.
In "On the Lam" Martin had a pet Koala Person who he named Martin 2. Martin 2 referred to Martin as "papa." Martin did care for Martin 2 but had to abandon him to save his life, similar to the reason why Martin abandoned Finn.
By the end of "On the Lam" Martin flew off in a Space Moth back into space. In "The Comet" he even called Finn his son and has changed a whole lot since he was first reunited with him. In The Comet, Martin even told Finn that "no answer I give you will be satisfying" when Finn confronted him about "fleeing the scene like a ding-dong ditcher in the night". Finn was given an option by the Catalyst Comet to live a new, cosmic form of life, but he declined. Martin chose it instead and said goodbye to Finn, and they ended on okay terms.
Finn no longer despises Martin, but doesn't particularly like him either. He seems to rarely mention him now, and when he does, he seems to refer to him more as "Martin" than "Dad". In the episode "Whispers", Finn describes Martin as not "evil incarnate", but "kind of a crummy dude".
Martin has mentioned Finn's mother briefly in "The Visitor," saying that talking about her stresses him out, and saying he might discuss her with Finn later (although he never does).
Finn manages to finally meet her in the second miniseries, "Islands". At first the mother and son are happy to be reunited, but soon Minerva tries to force Finn into abandoning his old life in Ooo to live on the island for the rest of his life. This causes him to rebel against her, and he rallies the inhabitants of the island and convinces them that they should be free. Minerva does not appreciate this, but Finn shows her memories of him helping people in Ooo and they reconcile. Finn and his friends spend a little more time on the island and with her. Eventually, he leaves for Ooo in good terms with her, hugging her, and even shedding a tear.
FernFern is Finn's grass clone who has all of his memories until the point he was created. He was created after the cracked Finn Sword touched Finn's Grass Sword at the end of "Reboot". This continued into "Two Swords." Initially, Fern was a grass humanoid but quickly took the appearance of a blocky Finn, made of grass. At first Fern believed that he was Finn (due to having his memories) and believed the actual Finn to be an impostor. However Finn and Jake both started yelling at Fern calling him a demon. Fern later, went to the Tree Fort, assuming it was his home. He then started getting frustrated with himself and made a giant mess. Finn and Jake then returned home. Jake was angry at Fern but Finn decided that he is not harmful and gave him a Finn Cake.
Later in "Do No Harm" Fern was depressed, sleeping on the roof of the tree fort. Finn had to run some errands and asked Jake to do "Finn stuff" with him. Fern was frustrated with the fact that we is unable to eat with his grass body and unable to breathe and could not play the flute. So, Jake took Fern to the grassy mountains. At the grassy mountains Fern met the Grassy Wizard, Fern however, lost his temper and attacked the Grass Wizard. Finn told Fern he did a good job. Fern decided he is not Finn (he had been referred to as "Grass Finn", etc.) and chose to be individual and became known as "Fern."
In "The Invitation", Finn who was going on a trip to the islands to find out about his species, asked Fern to cover for him while he is away. Fern doubted that he could do it but Finn said, he can, but do it "his way."
In "Cloudy" Finn tells Jake that he had a fear that Fern would be better than him.
In "Whispers" Fern and Finn are going fishing together. Fern is frustrated with the fact that he failed to protect Ooo while Finn and Jake were away at sea and the elemental spell took over Ooo until Finn came in to save the day. Fern was angry because he believed that he cannot do anything right while Finn can, making him jealous. Shortly after Sweet P comes running by screaming due to having dreams about The Lich, his true self. Finn and Fern try to calm Sweet P down but Fern said something that frightened Sweet P. This angered Finn. The dream was later revealed to be real and the Farmworld Lich/Jake. Finn went after it and Fern stayed behind and watched Sweet P. While Finn was away Fern was knocked out by Sweet P. At the end of the episode, Finn was walking Sweet P home and Fern was walking behind jealously looking at Finn.In "Three Buckets" Fern has knew ability allowing him to make himself appear identical to the real Finn. After showing Jake and BMO, Fern asks Finn to go on an adventure with him. Finn and Fern than play together on the walk over but Fern becomes frustrated after losing a game of rock-paper-scissors. Fern than shows Finn the destination, an old temple and its ruins. Finn tells Fern he really appreciates their friendship. Fern hesitates and tells Finn to go into a room ahead. Finn gets locked in a room and Fern reveals to Finn that he will keep Finn in there for the rest of his life, while he'll use his disguising powers and take Finn's place in his life. This angered Finn however, he quickly escaped with the help of his mechanical arm. Finn attacks Fern because of what he did. Fern than says things like "You've been Fern long enough." Fern than brings Finn to the ground, Fern was right about to kill Finn but, Finn accidentally used his mechanical arm and killed Fern by putting it into his chest and turning him from a being of grass into nothing but grass. Finn came home traumatized and sad from the incident.
A month later in "The Wild Hunt", Finn is feels so bad from "killing" Fern, despite the fact that Fern tried to kill him. Finn cannot kill any monsters because he keeps being reminded about how he killed Fern. However Huntress Wizard helps Finn get over this and said "[Fern] was a bad version of [himself] that [he] had to destroy." After the episode Finn gets over what happened to Fern.
In "Seventeen" a mysterious, green knight crashes Finn's birthday party. The knight challenges Finn to multiple games. In an arm wrestling match, the knight reveals that he is Fern making Finn upset. It was revealed that Gumbald had revived Fern with his remains and transformed him into the Green Knight.
BMO lives with Finn and Jake in the Tree Fort. It serves as their living video game system, film editor, camera, and many other portable electric items. They appeared in the eighth episode of Adventure Time, so they have been with the two for a long time. Occasionally, Finn and Jake seem to take on parental roles when it comes to BMO, such as taking them to soccer practice or disciplining them when they misbehave. Jake even calls BMO his and Finn's son in "Imaginary Resources".
In "Video Makers," BMO records the footage requested by Finn and Jake, although they disagree on what genre of movie it will be, so they leave BMO a note that tells them to keep only the best footage and present it at the Movie Club. BMO ends up bringing Finn and Jake together by using both the action and comedy/romance footage and singing a song, rather than taking sides with either of them. In "Incendium," BMO's video game music inspires Finn to sing "All Gummed Up Inside," then BMO helps watch him while Jake courts Flame Princess for Finn, and even pulls a kancho prank on him to try and cheer him up.
In "Be More," Finn and Jake help BMO by taking him to the place where it was born to find new core system drivers and preventing it from being wiped of its memories. It is also revealed that BMO was sent out to the world by Moe to find someone who can take care of it, and Finn and Jake were the ones sympathetic to adopt it.
Though he initially considers her an enemy in her debut, "Evicted!," Finn quickly befriends Marceline the Vampire Queen, as he learns that her seemingly evil ways are just playful teasing in "Henchman." A rowdy and adventurous character, Marceline and Finn share the same vigor and thirst for danger. One of the key reasons why they managed to forge a friendship is that Finn saved her life in "Henchman" when Jake exposed her to direct sunlight and threw garlic at her in a misguided attempt to save Finn. In the same episode Finn, in an attempt to convince Jake of her generally wholesome ways, calls Marceline "a radical dame who likes to play games."
Despite Jake's initial fear of Marceline (and of all vampires), Finn enjoys spending time with her so that they can be "awesome together." In "Go With Me", Finn asks her to go to "Couples-Only Movie Night," but only as a friend. Being mutually disgusted to the point of vomiting by the idea of kissing (although, ironically, she has kissed him on the cheek at least twice, albeit in only a playful manner), Marceline said no to Finn when he asked her to go to the movies thinking he was asking her to be his girlfriend. In "Marceline's Closet," he accidentally sees her naked when Jake tells him to see if the coast is clear for them to get out of her house, causing him discomfort.
In "Daddy's Little Monster," Marceline jests that she does not want hang out with him anymore, but it is implying that this claim is a jest when she invites him, Jake and the Ice King in a basketball game in her house in "Simon & Marcy."
Finn became friends with Lady Rainicorn after Jake wanted to hang out with both of them at once in the episode "My Two Favorite People." At first Jake regrets introducing the two, but in the end is glad it happened. Finn and Lady Rainicorn still share a close bond, despite the fact that Finn can't understand Lady Rainicorn's fluent Korean. In the episode "All the Little People," The toy versions of Lady and Finn are seen kissing, but then Finn laughs and says "weird" which implies that Finn knows nothing will happen between them. In The Pit, Finn asked Lady Rainicorn to help him save Jake from Kee-Oth in the broken dimension.
Finn looked up to Billy as a hero and friend. In "His Hero" Finn is shown to be willing to do anything to impress Billy, but at the end of the episode, he proved to Billy that it's needed to fight sometimes, and even gained his admiration and friendship. According to Canyon, Finn reminds her of Billy when he was younger, which could explain why they became fast friends, even to the point of a slight father-son relationship. Finn still gets traumatized about his death and even remembers that time when Billy single-handedly defeated a group of monsters.
Finn had a rather obvious crush, which he denied before the events of the episode "Wizard Battle," on Princess Bubblegum, whom he occasionally calls "Peebles" and other nicknames out of affection. He interacts with her more than any of the numerous other princesses of Ooo, and would jump at the chance to do anything for her. In a sense, their relationship was like that of a prototypical royal princess/loyal knight. After his heroic duties Bubblegum would, as Finn hoped, occasionally kiss him afterward, though she hasn't kissed him (or anybody else) since "Wizard Battle."
Finn becomes very protective and jealous when someone else comes between them, as seen in "Ricardio the Heart Guy," in which he obnoxiously performing the Science Dance as a desperate ploy to attract Princess Bubblegum's attention and sought to one-up Ricardio and expose him as a villain. Later on in The Suitor, Finn expresses his jealousy through a thinly disguised veil of contempt for Braco believing him to not be good enough for her. However, when he learns that Braco is still trying to win over the princess (i.e., that he hasn't succeeded) he helps him out by allowing Braco to perform Finn's quest.
In "The Real You," Princess Bubblegum becomes concerned about Finn and his new genius identity after donning the Glasses of Nerdicon during her Science Barbecue. She assures him that she only likes Finn as his normal self. Princess Bubblegum kisses Finn on the cheek for trying to win her heart through his smarts. In "The Duke," she shows that she could never hate Finn forever after he accidentally threw a bottle that made her green and ugly, implying that she has a deep friendship with him to not be able to break it.
Finn eagerly hoped to win the princess over with his heroic deeds. Finn and Princess Bubblegum share a staunch sense of morality and often work together to bring justice and balance to the Land of Ooo. Taking several dangerous and tomboyish cues from Marceline in "Go With Me," Finn tries to set up a movie date with Princess Bubblegum ultimately, by Marceline's advice, trying to "wrestle" her and by leading wolves into her bedroom, and the Princess regretfully banishes Finn from the Candy Kingdom until he stops "acting like a psycho."
In "Mortal Folly," when Finn and Jake are chasing the Lich, the Ice King persistently nags them to give him their blessing to marry Princess Bubblegum. When the Ice King says, "It's not like you want to marry her," Finn blushes and angrily throws a rock at him. Earlier in the episode, before embarking on their pursuit of the Lich, Princess Bubblegum gives Finn a pink sweater that she knitted for him, saying that she cares about him. This sweater would later protect Finn against the Lich using the "power of liking someone a lot," as Finn put it. He later refers to the sweater as his "like-like sweater."
In "Mortal Recoil," Finn outwardly confesses to the princess that he "likes her a lot," although it is unknown whether she actually heard him, as she was still possessed by the Lich at the time. Princess Bubblegum, whose incomplete reconstruction at the end of season two (resulting from the candy surgeons' inability to completely recover all the pieces of her bubblegum body) caused her to revert to her 13-year-old self, hugs Finn after her recovery and calls him "hero."
In "Too Young," she shows much affection towards Finn. Based on her actions, this may show that this might be Princess Bubblegum's actual feelings for him if she was at that age at the time. To complete her re-aging process they share "a whopping love-hug" and a kiss. Afterward, she can only remember the hug "was, like, five years ago." Finn feels beaten afterwards, but a pep-talk from Jake brings his spirits back up. In "Wizard Battle," Finn gets a kiss from Princess Bubblegum again (her last to date) after winning the Wizard Battle. She does this to reward Finn for going to such lengths to kiss her, and for stopping Ice King from kissing her. She slaps him shortly afterwards for cheating and ruining the sanctity of the event.
As of "What Was Missing," it is revealed that Finn has kept Princess Bubblegum's wad of hair from "To Cut a Woman's Hair" and spends quite a bit of alone time with it, as stated by Jake. She becomes aware of this as Finn reveals the secret in his song.
After being rejected several times, in "Incendium," Finn becomes deeply depressed and cries over Bubblegum by a little shrine he constructed made up of two framed pictures of her, his lock of her hair, and a pool of his tears. He becomes enraged and states that he'll kill whoever started a fire that burned his two pictures of Bubblegum. After his brief encounter with the Flame Princess (who started the fire) and saying that he likes her, and later saying that he thinks he has a crush, showing that he has gotten over Princess Bubblegum.
In "In Your Footsteps," Jake says that Princess Bubblegum was his ex-girlfriend, but Finn replies "we never went steady."
In "Burning Low," Finn thinks Princess Bubblegum is jealous of his new relationship after hearing this statement from Jake; this thought is boosted by her attempts to call off the relationship, but in reality she is trying to prevent global destruction from a disastrous reaction by Flame Princess's unstable elemental matrix. When he goes to write a poem for Flame Princess, Bubblegum finds him, and tries to explain to him that "responsibility demands sacrifice." She thought that Finn understands this, but Finn angrily reacts, in which he officially reveals his feelings for her before and is ready to move on.
In "The Suitor," when Princess Bubblegum states that Braco is a suitor of hers, Finn's face drops, saying, "Oh, cool. That's cool. You're dating. That's cool." Later, Braco asks Finn for the map to the soul stone, so that he can bring Princess Bubblegum the stone, in the hopes that she will love him. Finn then tells him that "that road you're on leads to nowhere," which might be referring to his former love for her.
In "Too Old," Finn seems to have gained interest in Princess Bubblegum again due to his break-up with Flame Princess. But by the end he realizes there is more of a difference between them besides just age. He now wants to talk to Flame Princess to try to fix what he caused.
In "Rattleballs," Finn has decided to get out of his last relationship by protecting Bubblegum and following her commands. Though it was unknown if he was dedicated to Bubblegum again, he did it in an embarrassing and intrusive manner that annoys her. He also states that he served her one hundred percent like how the gumball robots were programmed. When she mentions that she's out of milk, he goes overboard and spends three weeks getting a tiny vial of special mink's milk. Later at the junkyard, he has fashioned a scrappy Bubblegum mannequin out of garbage and pretends to defend its honor, referring to it as "my lady."
In "The Pajama War" Finn and Princess Bubblegum spend time as good friends and somewhat flirt with each other. They hung out and made it work, despite their age difference.
In "Don't Look" Finn (who had the cursed eyes that turned others into what he saw them as) turned Princess Bubblegum into a "boy" which implies that he may see her more as a friend now rather than a romantic interest.
In "Hero Heart", after becoming a fire person under the elemental spell, Finn acts very hostile and violent, like all the fire people. Finn was right about to harm Princess Bubblegum (who was in her elemental form) but Lumpy Space Princess stopped the attack and called PB "a person he loves." LSP then takes a piece of PB's gum, and places it on Finn's face hoping it would be his "happy place." In this state Finn remembers the old times with Bonnibel back when he had romantic feelings for her in episodes such as "To Cut a Woman's Hair" and "Too Young". However Finn becomes a little embarrassed by these memories and becomes happier remembering more recent times with her, in episodes such as "The Pajama War" when he sees her more as a friend. This supports the fact that Finn probably is completely over his Princess Bubblegum romantically.
Flame Princess was Finn's first girlfriend, and currently, ex-girlfriend. He first meets her at the end of the episode "Incendium." During the episode, Jake poses as Finn trying to court her because he believed that Finn, depressed after being rejected again by Princess Bubblegum, needed a new love interest. However, when Flame Princess's father tells Jake that she is evil, Jake tells her (disguised as Finn) that he doesn't like her, which causes her to become confused and angry, consequently attacking him and following him back to the tree fort where the real Finn is.
She starts a fire in the house which burns the pictures in Finn's shrine to Princess Bubblegum, and he becomes enraged and runs to see who ruined his shrine. When she accidentally lights the liquid pyrotechnics left behind by Princess Bubblegum and douses her fire, he saves her and brings her into the house. When she regains consciousness, Flame Princess yells at him, "You! What's wrong with me, huh?! You don't like me?!" and Finn states, "I like you!" This statement, despite Finn never knowing Flame Princess before, however, is not evident of "love at first sight.", and shows Finn's naivety and immaturity, immediately forgetting his despair over Princess Bubblegum's rejection just moments before. Flame Princess blushes, then slaps Finn and warns him never to mess with her again, and flees the tree house. After she slaps him, he immediately wanted to know who she was. He then told Jake, "Dude, I think I have a crush."
In the continuation episode, "Hot to the Touch", Finn asks Jake to help him find her, saying that he "peeped beyond her burning gaze" and that "she ain't evil," and the two run out to look for her. They find her by a pond and hide behind bushes. Finn describes her metaphorically as "the steam off a puppy's nose searching for ham in snow" and "a cute little flower." When she curiously dips her hand in the pool and jumps back in pain, Finn rushes to her aid, surprising her. Finn admits to Flame Princess that he really likes her and they should be together, which causes her to glow brighter and makes small fires appear around her. Finn is surprised with the fire getting near him, so he tries to put them out, not knowing that by putting out the flames he would hurt Flame Princess.
Despite the initial animosity between them, their relationship improves near the end of the episode. Finn, angry and upset that he can't "just like a girl," begins to cry. One of his tears fall on one of the fires Flame Princess had created, evoking her attention. Flame Princess watches Finn cry, both confused and amazed. She states that she now understands that Finn is a Water Elemental because he "creates water". Flame Princess says that no matter how much they like each other, they can't be together because they will merely hurt each other. Finn replies, "No, I can take it. I mean...we can try." Flame Princess glows, touched that he "would defy nature" for her. She hugs him, and although he smiles for the first few seconds, Finn begins to burn up and pushes her away. Flame Princess says goodbye to him and departs.In "Burning Low," she and Finn are officially a couple. Their relationship has improved for the better since their last interaction. In the episode, they hug for the first time, with Jake subsequently attempting to educate Finn on the "tiers" of dating. When Princess Bubblegum tells Finn that he should stop seeing Flame Princess, he reacts angrily, thinking that she is jealous. This somewhat shows Finn's overprotective nature over his relationship with Flame Princess. Jake is also angry at Princess Bubblegum, as he believes that she is trying to sabotage their relationship, when he just wants Finn to be happy. Princess Bubblegum explains that extreme romance, such as kissing, will cause Flame Princess's elemental matrix to become unstable and burn the planet from the inside out. He and Princess Bubblegum then try to stop the kiss, but arrive to see them already kissing. When Flame Princess falls into the earth's crust due to her instability, Finn heroically leaps in to save her. He holds the unconscious Flame Princess in his arms and states "I need you to be okay". After using artificial respiration to revive her, they continue to date. This whole episode displays Finn's deep affection for Flame Princess, and his selfless desire to continue loving her despite the dangers to himself.
In "Ignition Point", Finn's affections for Flame Princess go as far as questioning the Flame King about her affiliation. Despite the Flame King insisting his daughter is evil, Finn protests and asks if it were possible to change her to good, indicating his concern over Flame Princess' well-being.
In "Reign of Gunters", however, Finn takes the advice of a dating book called Mind Games and tries to act more mysterious, claiming he needs to keep all the ladies in a state of confusion; that way, he has "options in case Flame Princess doesn't work out", suggesting that he is not fully confident on his relationship with Flame Princess, and plans ahead in case they split up instead of being positive, further highlighting the credulity that he feels inside.
In "Vault of Bones", Finn is determined to convert Flame Princess to good. They go to a dungeon together, with Finn teaching her how to properly dungeon crawl. She thinks his methods are boring, and, due to her destructive personality she opts to just burn through everything with her elemental powers, causing Finn to feel slightly uneasy. However, when Finn is captured by a Giant Goo Skull, Finn warns Flame Princess not to use fire to defeat it, and although Finn thought she was going to incinerate the Giant Goo Skull and harm him in the process, she instead intimidates the monster as Finn had done earlier on. She assures Finn that she'd never hurt "[her] boyfriend," and afterwards, she says that she had a great time.
In "Puhoy," Finn says that he told Flame Princess a joke, but she didn't laugh, which causes Finn to worry about the status of their relationship, showing his innocence and inexperience, becoming somewhat paranoid that Flame Princess no longer likes him. Upon returning from the Pillow World, Flame Princess calls him, saying that she finally got his joke, and she thought that it was funny, rekindling Finn's affections.
In "Jake Suit," it is shown that Flame Princess wants to introduce Finn to her less evil family members, but due to Jake's manipulation of Finn, he embarrasses himself. Flame Princess goes outside and confronts Finn in anger and bewilderment, but then discovers that Jake is controlling him. Even though Flame Princess admires how Jake tries to cause Finn pain, she ultimately wishes Finn good luck and victory.
In "Frost & Fire," after Flame Princess beats up Ice King, Finn begins to dream about the fight, however he keeps waking up before the dream ends. In order see the dream's outcome, he continues to pit Flame Princess and Ice King against one another by writing insulting messages about them and claiming the other sent it. The Ice King and Flame Princess have battle in the Ice Kingdom, which eventually melts because of Flame Princess' powers. Finn passes out from the heat and the dream ends with the Cosmic Owl saying he "blew it." After Finn awakens to Flame Princess on a rampage, he goes and saves the defeated Ice King and admits to sending the letters. This betrayal and the hurtful things in the letter that only Finn would know about causes Flame Princess to walk off, saying she needs some time by herself. Ice King repeats to Finn that he, indeed, blew it.
In "Too Old", Finn seemingly moved on with the breakup with Flame Princess, but was short-lived as he failed to restore his past relationship with Princess Bubblegum and realises that there is just too many differences between them to ever have a real relationship. He then come to terms with how much he messed up with Flame Princess and decides to talk to her soon and fix what he has done, but gets nervous when Jake jokingly states that she might have a new boyfriend by now.
In "Earth & Water", when Finn apologises to Flame Princess, she accepts it, although still visibly hurt by his actions. In response, Finn asks if they are still going out. Flame Princess says no but that they can be friends. She tells him he can visit her any time in the Fire Kingdom as long as he is completely honest with her, and he looks upset - but nods in agreement.
In "The Pit", he states that he still loves Flame Princess. By this time, Finn's despair over Flame Princess is evident of the start of his maturation later on in the series.
In "Red Throne", Flame Princess asks Finn to help her reclaim the Fire Kingdom after a coup by Flame Lord and Flame King. However, Flame Princess states that she no longer has any feelings for Finn. Finn tries to impress her by showing off his grass sword, improved swordsmanship, and updates into his personal life during their journey to the Fire Kingdom. Later, Cinnamon Bun saves both Flame Princess and Finn. Cinnamon Bun then admits his love for Flame Princess and vows to fight alongside her. Finn mutters "Geez, did I just get shown up by Cinnamon Bun?".
It is stated in "Breezy" that Finn no longer talks to Flame Princess, which implies that he believes she and Cinnamon Bun are dating. Which was confirmed not to be true by the writers and Cartoon Network's Official Twitter Page.
However, in "The Mountain", while Finn is looking through his telescope, he spots Flame Princess rehearsing a dance with Cinnamon Bun. His reaction is that of slight longing, and perhaps contempt, igniting his decision to follow Lemongrab up the mountain, in order to distract himself from seeing his ex-girlfriend. Flame Princess also appears in the mirror as one of the three choices along with a butterfly and BMO with Jake, indicating that Finn might still have feelings for her, or isn't over her just yet.
In "The Comet", the Catalyst Comet states many features of Finn's life. The first of which is "love", and a cameo of Flame Princess appears, which is hinting that Finn had loved Flame Princess before, or Finn still hasn't gotten over her.
In "Bun Bun" Finn finally apologises whole heartedly to Flame Princess, showing his maturity and sincerity, with Flame Princess stating "You've grown up a lot, man." Finn and Flame Princess restore their friendship by hanging out together, beat boxing and rapping.
In "Happy Warrior" when Finn and LSP sneak into the Fire Kingdom, LSP asks Finn if he is still into Flame Princess; Finn answered "No. FP and I are just friends. And I'm really proud of that friendship. Getting there took a lot of trust building and emotional growth." When Finn first encounters Flame Princess, not recognizing her on account of her new elemental appearance, he became furious due to mistakenly assuming that Flame Princess was eaten. This suggests that Finn still cares about Flame Princess. LSP remarked "Honestly, I can still see those two working out," as she watched cursed Finn and Flame Princess—as a dragon—fight each other.In "Son of Rap Bear" Finn and Flame Princess casually hang out together throughout the episode. Finn wants to help her keep her kingdom after, signing a no-good contract to Toronto. He helps Phoebe in win a rap battle with Son of Rap Bear.
RoselinenIn "Puhoy," Finn meets Roselinen, his third love interest, in the possibly-imaginary realm of the Pillow World. Finn enters this realm to let his mind unwind, as he is having supposed relationship problems with Flame Princess; when he meets Roselinen, she asks him to dance, to which Finn replies "I have a girlfriend." She insists that the gesture is purely platonic, and they dance. As they talk, she shows signs of liking him, and Finn talks half-embarrassed.
Eventually, as by this time, Finn believes there is no way to escape the Pillow World, Finn abandons his relationship with Flame Princess to start a new life with Roselinen, having two kids named Jay and Bonnie. When Finn finds out there is a way to escape the world, he is fully willing to go, though torn up about leaving Roselinen and his family behind. Roselinen asks Finn to not forget about them. Finn grows old and returns to his world at the point of his death in the Pillow World. When Finn returns to his world, he is about to tell Jake about his "dream," when Flame Princess calls to say she gets his joke. After Finn tells Jake about his phone call, Finn forgets all about the dream, and also forgetting Roselinen and his family in the process.
In the episode "Breezy", a to-be-queen bee, Breezy, is attracted to the flower where Finn's arm used to be. As time progresses, she discovers that she not only likes Finn's flower, but has a crush on Finn himself. When Finn is threatened by the other bees, Breezy drinks the "royal jelly" to transform into the rightful queen bee of the hive and save him with her new-found powers. She confesses her love for him, but Finn declines the offer to be with her, stating that the feeling is simply not mutual, highlighting his insensitivity and carelessness at the time.
Erin is Finn's non-canon love interest whom he meets in "Food Chain." Finn immediately falls in love with her beauty the moment he saw her. After a short interaction with each other, they jump to a quick conclusion to get married. At their marriage, Finn was nervous at first with Erin's beauty and as they were about to kiss, a pair of birds suddenly came and attacked the caterpillars. Finn and Erin tried to escape, but went flying then falling. Before Finn went back to normal, he vowed to Erin that he'll marry her again when they meet again in a different lifetime. When Finn turns back to normal, it is unknown what happened to her.
Huntress Wizard is Finn's secret love interest with whom he interacts in "Flute Spell", in which he tried to help her by summoning the Spirit of the Forest. After many failed attempts (Finn had been absent for some time as stated by Jake), they succeeded when they played their flutes together and the Spirit finally appears. The Spirit then asks Finn who is he really playing his Flute Spell for. After some hesitance, Finn answered that it was for Huntress Wizard, and confesses his secret feelings for her, stating that he was going to play the Flute Spell until his "flute broke". Huntress Wizard is amazed but disheartened at the same time, due to her beliefs involving romantic relationships, revealing that she is not ready to commit. Despite this however, she also unveils her affections for Finn by kissing him, shocking Jake, and admitting that her flute spell was for him as well, and revealing her attraction to his hair and calling him an "exceptional beast". However, being "exceptional beasts" means that they can't fall in love, to which Jake responds with "that's real dumb". Finn then states his agreement, however it is ambiguous as to whether he agrees with Jake, Huntress Wizard, or both. With this, Finn has matured greatly since his relationship with Flame Princess. He is shown to be much more cautious with his feelings and did not rush to earn Huntress Wizard's affections.
In "Wheels", Huntress Wizard appears and listens to Finn as he starts playing the flute, before retreating back to hide, indicating that she still has feelings for him.
In "The Wild Hunt", Huntress Wizard saves Finn by deflecting the hot fudge from the Grumbo and carries him in search of the said creature. While tracking the Grumbo, she notices Finn's hesitation of slaying the creature and decides to both help him on his mental block and hunt down the creature together. As they found the Grumbo's lair, Huntress Wizard constricts the creature with her vine and lets Finn give the final blow, reluctant, Finn could not kill it and resulted on both of them getting injured. With Huntress Wizard in danger (who was actually pretending) gives Finn the push he needed to slay the Grumbo. After the Grumbo was slain, they finally accept each another's feelings as they nonchalantly exchange a kiss.
Music Hole is a sentient hole in the ground who Finn meets in "The Music Hole". At the end of the episode, the pair sing a duet and Finn plants a kiss just below her mouth, which makes her strongly blush.
The Lich's desire to kill off life brings him into constant conflict with Finn. They first meet in "Mortal Folly," although it is implied in "His Hero" that Finn already knew about the Lich, where the Lich is freed from his prison, goes on a rampage and tries to regain his power to destroy all life. In the episode, the Lich tries to dip Finn in his Well of Power, implying that the Lich believes Finn should be on his side. He also states that he believes Finn is his inferior.
The Lich was shown trying and succeeding in manipulating Finn's emotions to his own gain several times. This was first shown in "Mortal Recoil," where the Lich (disguised as Princess Bubblegum) manipulates Finn's romantic emotions toward Princess Bubblegum and makes him hand over the things he needed to regain his powers and continue his quest to destroy all life in the Multiverse. Later, in "The Lich," the Lich (disguised as Billy) uses Finn's trust of Billy and makes Finn get the gems of power, which he connects with the Enchiridion and uses to travel to the center of the multiverse and the wishmaster Prismo.
As a recurring antagonist, Ice King is frequently at odds with Finn. Finn is prone to impatience and aggression around him but also shows him sympathy, as in "When Wedding Bells Thaw." However, Finn's aggression never outweighs his compassion, honor, and respect for life, as evidenced when he refused the opportunity to slay Ice King as Billy had slain the Fire Count. Similarly in "Mortal Recoil," Finn, albeit grudgingly, trusted and united with Ice King against their common enemy of the Lich-possessed Princess Bubblegum. The Ice King competes with Finn for Princess Bubblegum, which is one of the sources of antagonism between them. This mutual attraction for Princess Bubblegum can be clearly seen in "Mortal Folly," where Ice King continually pesters Finn for consent to wed Princess Bubblegum. Upon Ice King's saying, "It's not like you wanna marry her," Finn blushes and hurls a rock at Ice King.
Finn and Jake sometimes appear to spy on the Ice King the Ice King like in "I Remember You," and "Chamber Of Frozen Blades," which in both situations, they were spying on the Ice Kingdom, and more extremely so in "Chamber Of Frozen Blades," where they actually go into the Ice Palace and search for signs of captured princesses.
Although Finn and the Ice King began as bitter rivals, their relationship progressed in the later episodes to a friendly rivalry, then an odd friendship in its own right, and finally a genuine friendship.
The Ice King does not really hate Finn and Jake, as he only fights with them because they are morally opposed to each other. He frequently tries to be friends with them, in his own, misguided ways, and has willingly made alliances with them. In the episode "Still," the Ice King freezes Finn and Jake so they can have "bonding time." It was shown in "Hitman" that while Finn and the Ice King are rivals, they are not enemies, and don't harbor any real malice towards each other. The Ice King made it clear that he doesn't want to kill Finn, the most he would do is punch him in the belly and make him vomit up his lunch. At worst, they are battling rivals, as Finn openly disapproves of the Ice King's habit of stealing princesses and causing mischief. At best, they are playful rivals, even friends.In "Holly Jolly Secrets Part II," the Ice King has a locket with the pictures of Finn and Jake. Near the end of the episode, the two are shown snuggled up side-by-side by a roaring fire, wearing ugly Christmas sweaters. Finn's attitude towards the Ice King has softened since discovering the tragic secret of his origin, and his compassion for people in distress outweighed his petty squalls with him enough to be his friend.
In "Mystery Dungeon", Finn is shown to kind of finally understand how sad Ice King is.
In "Beyond this Earthly Realm," Ice King tricks Finn into putting all the creatures of the spirit realm into the spirit hole, saying Finn would be freed from the spirit realm if he did so. However, when Ice King accidentally falls on the porcelain lamb, Finn and Ice King help each other to be freed from the spirit realm by affecting the material plain and breaking the porcelain lamb.