The dragon itself could be the main character. It could be a young dragon trying to learn about the world outside of its lair. It comes to the Adventure Time school to learn more about magic, friendship, and how to co - exist with different creatures. It would have to face its own fears and insecurities while making new friends like Finn, Jake, and Princess Bubblegum.
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.
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'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.
Trunks could also be a main character. He's from the future and has a cool attitude. In the fanfiction, he could be the new kid at school, trying to fit in while also having to deal with threats from his own time that somehow follow him to the school.
Finn, a brave and curious human, and Jake, his magical dog buddy, are central to Adventure Time main story. Princess Bubblegum is another important character. She's intelligent and has to deal with the governance of the Candy Kingdom. The Ice King, with his ice powers and his obsession with kidnapping princesses, is also a key figure. There's also Marceline the Vampire Queen, who has her own unique personality and backstory that ties into the main story in various ways.
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 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.
Probably Finn and Jake, as they are the main characters in most Adventure Time stories.
The main characters are Finn the human and Jake the dog. Finn is a fearless adventurer, and Jake, with his shape - shifting abilities, is always by Finn's side. Also, Princess Bubblegum, who rules the Candy Kingdom, is an important character. And the Ice King, who often causes problems for Finn and Jake.