Obviously, the Hot Dog Princess herself is a main character. Finn and Jake might also be main characters if the fanfic is set within the broader Adventure Time universe and they interact with the Hot Dog Princess. Other possible main characters could be the villains or sidekicks that are specific to the Hot Dog Princess' story, like her royal hot dog guards or an evil chef who wants to steal her hot dog recipes.
In most adventure time hot dog princess fanfic, the Hot Dog Princess is a key main character. If the fanfic is about a war or conflict, then the leaders of the opposing sides could be main characters as well. For example, if there is a war between the hot dog kingdom and the ice cream kingdom, the Ice Cream King could be a main character. Also, if the fanfic focuses on a love story, then a love interest for the Hot Dog Princess, perhaps a brave knight or a wandering minstrel, could be a main character.
One idea could be a story where Hot Dog Princess goes on a quest to find a magical ingredient to make the best hot dogs in all of Ooo. Another could be about her making friends with a new character who doesn't understand the concept of a hot dog princess at first. Maybe a fanfic where she has to defend her hot dog kingdom from an invasion by some sort of food - hating villains.
The Ice King can also be a part of adventure time bandit princess fanfiction. He might try to capture the Bandit Princess for his own strange reasons, like wanting her to be his ice princess. His bumbling nature and ice powers create comical and challenging situations in the story.
Obviously, Finn and the Jungle Princess are the main characters. Finn, a brave and adventurous boy, and the Jungle Princess, who has her own set of skills and knowledge about the jungle environment.
The main characters are Finn, a brave and adventurous human boy, and the Water Princess. Finn is known for his heroics and his sword - fighting skills. The Water Princess has control over water and is from the Water Kingdom.
The Ice King could be a great antagonist. He might be jealous of the Water Princess's power over water and try to freeze all the water in her domain. His craziness and his desire for power could drive him to do this.
Often, Finn and Jake might make appearances in Adventure Time Gum War fanfic as they are main characters in the original series. They could be involved in the Gum War in various ways, like trying to stop it or getting dragged into it. Princess Bubblegum is also likely to be a main character as she has a lot to do with gum.
Blake and Leo are the protagonists. They might be friends or siblings who decide to embark on adventures in the Adventure Time world. Since it's a fanfic, they could have unique personalities and abilities that set them apart from the regular Adventure Time cast.
Since I don't know the specific 'hot dog graphic novel', it could have a hot dog as the main character. Maybe it's a hot dog with a personality, like a brave or a comical hot dog.
Since I don't know the exact 'hot dog stand story', it could be the owner of the stand as the main character. They are the ones running the show, making the hot dogs, and dealing with customers.
Obviously, the hot dog guy and Gumball would be the main characters. The hot dog guy could be a street vendor type character with a big heart and a lot of stories to tell. Gumball, on the other hand, is his energetic and curious self, always ready to jump into new situations.