One idea could be Finn and Jake starting a new school year at a magical school in Ooo. They could have adventures while trying to pass their classes like Magic 101 taught by a wizardly character. Another could be Princess Bubblegum enrolling in a science - focused school to learn more about advanced chemistry and creating new candies. Maybe Marceline could attend a music school in the Land of Ooo where she discovers new ways to play her ax - bass and meets other musical creatures.
Well, you could have a fanfic where the Ice King decides to become a teacher at a school in the Ice Kingdom. He tries to teach the students about his 'ice magic' but ends up causing chaos. Or there could be a story about a new student from another dimension arriving at the school in Ooo and Finn and Jake have to show them around and protect them from the various dangers. Also, a fanfic about Lady Rainicorn teaching a foreign language class at the school would be interesting.
You could write a fanfic where the guardian angel loses its powers for a while. This would create an interesting situation as it has to rely on the help of others in the Land of Ooo. It could also lead to character development as it discovers new things about itself and the world without its angelic abilities. Maybe it forms new friendships or realizes the true value of certain things.
One idea could be a fanfic where Finn and Jake discover a new, mysterious land full of strange creatures that have powers they've never seen before. Another could be a story about Princess Bubblegum's early days as a ruler, like how she built the Candy Kingdom from the ground up. Or perhaps a fanfic that focuses on Marceline's relationship with her father and how it affected her growth as a vampire.
You could create a fanfic where Finn and Jake have to go on a mission to a completely new and unknown land in the Adventure Time world for your FRT fanfic. They might encounter strange new creatures and have to use their wits and powers in ways they haven't before. Maybe they find a land where the rules of magic are different, and they have to adapt quickly.
A great adventure time genderbend fanfic idea could involve Lumpy Space Princess as a male. He could be really vain in a different way, perhaps more focused on his muscles or some other masculine trait. And for Flame Princess, if she were a male, his relationship with Finn would be really different. Instead of the love - hate relationship they had, it could be more of a bromance, with them competing in feats of strength or something similar.
One idea could be that Breezy gets lost in the Land of Ooo and Finn and Jake have to help her find her way back home. Maybe she has a special mission that she needs to complete but can't without their help.
One idea could be a story where Fionna and Cake find a magical portal that leads them to a parallel universe where all the characters have swapped genders. It would be a really fun and unique take on the Adventure Time world. Another idea is that they go on a quest to find the rarest ingredient for a cake that has the power to grant wishes. They could face many challenges along the way, like battling new and strange monsters.
A fanfic could explore the relationship between Ooo and Aaa more deeply. Maybe they get into an argument over how to handle a new threat in Ooo, and through their differences, they learn more about each other and strengthen their friendship.
Perhaps there's a mystery in the high school. Marceline, being the cool and mysterious girl, teams up with Finn to solve it. They discover that there's a secret club in the school that's causing all kinds of strange happenings, like making students' lunches disappear or changing the school's layout at night.
One idea could be a new student arriving at the Jungle School who has a mysterious power. This could cause chaos and also intrigue among the existing students like Finn and Jake. Maybe they have to figure out if this new student is a friend or a foe.
Another plot could involve a new dragon teacher at the school. This dragon teacher has a very different teaching style compared to the others. For example, instead of using books, it teaches magic spells through real - life experiences. The students, including Finn and Jake, are both excited and a bit scared of this new way of learning.