In some Adventure Time fanfictions, Finn might be betrayed by a character he trusted deeply, like Jake. For example, Jake could make a deal that goes against Finn's values in order to protect the Candy Kingdom, leaving Finn feeling betrayed as he sees it as a moral compromise. Another instance could be a new character in the fanfiction who befriends Finn only to steal his magic sword for their own gain.
Well, Finn's real story is that he's a hero in the Land of Ooo. He's constantly on the move, exploring different parts of the land. He was raised in a rather unique environment, which has made him brave and curious. Finn has this unwavering sense of justice. For example, he'll always stand up to bullies like the Lich. His relationship with Jake is a big part of his story too. They're like brothers, always having each other's backs in any dangerous situation that they encounter during their adventures.
One idea could be that Finn is kidnapped by an old enemy who wants to use him as a bargaining chip against Princess Bubblegum. Maybe they demand her to give up the Candy Kingdom in exchange for Finn's safe return.
One possible scenario in this fanfiction could be that Finn's transformation into a vampire brings out a whole new side of his personality. He might struggle with his newfound thirst for blood while still trying to uphold his heroic values. Maybe he teams up with Marceline, who is already a vampire, and she teaches him how to control his urges.
He might meet some of the more reclusive characters in Ooo that we don't usually see in the show. Maybe a hermit - like wizard who gives him some cryptic advice.
First, establish the kidnapper's motives. Is it for revenge? Power? Or something else? For example, if it's for revenge against Finn's heroic deeds, it gives a strong starting point.
Princess Bubblegum would be a great addition. She could offer her scientific knowledge to help Cake and Jake in their adventures. For example, if they encounter a strange chemical reaction or a mechanical problem, she could come up with a solution. Finn is also a good choice. His bravery and sword - fighting skills would be useful when they face dangerous situations. And Marceline the Vampire Queen could add an element of mystery and her vampire powers might come in handy at times.
One great theme is their friendship adventures. Stories that focus on their new quests and how they support each other through different challenges are always interesting. Another theme could be how they grow together as characters over time.
He could cry due to unrequited love. Finn has had his fair share of romantic interests in the show. In a fanfic, if the girl he loves doesn't return his feelings, it would be a heart - breaking situation for him. Also, in some fanfics, Finn might be confronted with the harsh reality of the world he lives in. Maybe he discovers something truly dark about the Land of Ooo that shatters his innocent view of it, causing him to break down in tears.
One common theme is the exploration of relationships. Finn, being the central character, has to navigate through multiple relationships with different characters in the harem. Another theme is character growth. As Finn deals with the harem, he often grows as a person, learning about different personalities and how to interact with them.