Mr. Satan could also be a main character in a comical sense. He might try to take credit for dealing with Buu or get involved in some misadventures while the real heroes are fighting. And of course, Kami and Dende could play important roles as they are the ones who can sense the power levels and give guidance to the Z - fighters.
Obviously, Buu and Cell would be main characters.
Perhaps the fanfic is about Buu waking up and being confused by the events of the Cell Saga. He might not understand the conflict between the androids and the Z - fighters. So, he could start interacting with different characters in his own strange way, like befriending some of the minor characters or causing unexpected mayhem just because he doesn't know any better.
There could be the jailer who is in charge of the cell. Maybe it's a new character created for this fanfic.
In this 'buu wakes up in cell sags fanfic', Buu might wake up disoriented in the cell. He could start to explore his surroundings and find that the cell has some sort of magical or technological elements that are preventing him from leaving easily. As he tries to break free, he might encounter different challenges. There could be traps or puzzles that he needs to solve. And perhaps his waking up in the cell is part of a bigger plan by some powerful being, and Buu has to figure out what that plan is and how to stop it.
Maybe it's an old enemy who has somehow survived and is now more powerful. They could be seeking revenge on Captain America for past defeats. For example, Red Skull could have found a new way to return and cause trouble.
Obviously, Harry would be the main character, just in a female form. Hermione would also be a very important character. She could be the one to help Harry understand and navigate the new experiences of being a girl in the wizarding world. Ron might also be there, and his reactions to Harry's transformation could add some interesting dynamics to the story.
The main characters could be the protagonists from 'A Good Time'. They are likely to be the ones facing the situation within the cell.
New and upcoming writers could also write a great one. They might bring a fresh perspective to the idea. Maybe a young writer who has a vivid imagination and is a big fan of both Harry and Gabrielle as characters. They could come up with unique scenarios and interactions between the two that we haven't seen before.
She might be an old friend of Harry's from his childhood in the Muggle world that he didn't know was a witch. She had been suppressing her magic for a long time and fainted when it finally burst out uncontrollably. Harry wakes her up and helps her understand and control her new - found powers.
Well, Goku is surely one of the main characters as it's related to the Cell Games. He is the central figure in the fight against Cell.
One possibility is that he wakes up and discovers new allies. The story could then revolve around him building relationships with these new characters while still holding onto his old values. He may also have to deal with the fact that the world has moved on without him and find his new place in it.