In Adventure Time: Escape from the Citadel fanfiction, the main characters would include Finn, who is always ready for a quest. Jake, with his unique abilities, would be by Finn's side. Princess Bubblegum, being a powerful and intelligent character, could be part of the story, either helping from afar or being trapped in the citadel herself. Marceline the Vampire Queen might also show up, especially if there are some dark secrets or powers involved in the citadel. And let's not forget BMO, who could provide some comical relief and maybe even some useful gadgets or information during the escape.
The key plot points often revolve around the motivation for escaping the citadel. In the Adventure Time universe, it could be that something precious is held captive there, or there's a threat that looms over the characters if they don't escape. As the characters move through the citadel, they might encounter old friends or foes who either help or hinder their progress. There could also be a race against time, as the citadel may be self - destructing or something equally dangerous is about to happen, adding to the tension of the escape.
I'm not familiar with the specific 'the citadel novel', so it's hard to name the main characters. However, it's likely that there are characters associated with the citadel in important ways. There might be an architect who designed it, and a young hero who discovers something extraordinary about the citadel. Maybe there are also antagonists, like invaders or traitors within the citadel.
Since I don't know the exact 'citadel novel', it's hard to say. But generally, there could be a brave hero who is on a quest related to the citadel. There might also be a villain who wants to take over or destroy the citadel.
I don't know the specific main characters in this novel as I haven't read it.
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.
A young and brave adventurer could be a main character. They are eager to explore the unknown and end up in the middle of the darkness. Their courage and determination to find a way out would drive the story. Another could be a wise old wizard who has some knowledge about the darkness but needs the help of others to fully escape it.
Obviously, Harry Potter is one of the main characters. He is likely to be the driving force behind the attempt to get Sirius Black out of Azkaban.
There could also be new human characters created specifically for the fanfiction. These could include leaders among the humans, or characters with unique skills or personalities. For example, a human scientist who is eager to explore the magic of Ooo, or a young human who befriends the magical creatures right away and becomes an ambassador of sorts between the two groups.
Well, the si gamer is obviously one of the main characters. Then there could be Finn and Jake who might interact with the si gamer. Finn with his adventurous spirit and Jake with his shape - shifting abilities would make for interesting interactions with the si gamer.