Princess Bubblegum's future self could be a main character. She might be leading a resistance against a new tyranny in Ooo. Also, the Candy Kingdom could have new heroes from within its walls, like a young gumdrop who discovers a hidden power within herself and becomes a key figure in the future battles. Additionally, a future version of Marceline could be involved, perhaps she has become a mentor to the new generation of adventurers.
Princess Bubblegum could be a part of the fanfiction. She might be interested in the unique flora and fauna of the Canyon and could send Finn on a mission there. Marceline the Vampire Queen could also be added. Maybe she has some history with the Canyon and her presence could add an element of mystery and danger.
The main character could be a new, original princess. She's from a far - off jungle kingdom and has unique abilities like being able to talk to the spirits of the jungle. Jake could be her sidekick. He's always up for an adventure and his shape - shifting abilities could come in handy when they face different challenges in the school, like getting through mazes or fighting off small monsters.
Finn and Jake are obvious choices. Finn's brave and adventurous nature would make him a great character to explore the Jungle School's mysteries. Jake's shape - shifting ability could come in handy during various situations at school, like sneaking into restricted areas or helping in physical challenges.
Princess Bubblegum would also be a great main character. She's intelligent and resourceful. If there was a dragon in the school, she could study it scientifically, or try to find ways to use its powers for the good of the Candy Kingdom which the school might be a part of. And she could also be in charge of making sure the dragon doesn't cause any chaos.
A young scientist would be a great main character. They could be curious about what the future holds for their research and accidentally stumble upon a way to travel to the future. Their scientific knowledge would help them understand the new technologies and concepts in the future world.
Naruto's children would likely be main characters. They would inherit his strength and determination. Also, the students of the new generation of ninja academies could play important roles as they strive to make their mark in a world shaped by Naruto and his peers.
The main character could be an android. In this future, androids have gained sentience but are still treated as second - class citizens. This android starts a revolution to gain equal rights for all artificial beings.
The Ice King can be a key character too. Maybe he tries to kidnap Minerva for his own strange reasons, thinking she can be his new princess. Marceline the Vampire Queen could also be involved. She might be Minerva's ally or foe depending on the plot of the fanfiction. There are also other minor characters from the Adventure Time series that can play important roles in Minerva - related fanfictions.
Obviously, Shoko is a main character. She is often depicted as a tough and resourceful girl with her own set of skills. Another important character could be Finn. Finn might cross paths with Shoko and they could either become friends or rivals depending on the plot. Jake, Finn's loyal dog, could also play a role, perhaps helping or hindering Shoko's plans.
Finn and Jake would be obvious choices. Their courage and friendship could be put to the test in the harsh post - war world. They might be on a mission to help the survivors or to uncover the secrets of the war.