The main character is Harry in her new female self. Luna Lovegood could be a significant character in this fanfic. Luna has a unique perspective on the wizarding world, and she could be very accepting of Harry's transformation. Additionally, Draco Malfoy could be in the story. His relationship with Harry, which was already complex when Harry was a boy, could become even more so with Harry as a girl.
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.
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.
Obviously, Harry and James are the main characters. But there could also be Lily, Harry's mother, who would play an important role in his upbringing. Sirius Black might also be around a lot, as he was James's best friend.
Well, perhaps a plot where Harry wakes up as a girl and discovers new magical abilities that are more commonly associated with female witches. She might then have to learn how to control and use these abilities while also coming to terms with her changed physical form. It could also involve a romantic sub - plot where characters who previously saw Harry as a boy now have different feelings towards her as a girl.
Hermione would likely be a key friend. She might be initially very confused and try to analyze the situation rationally. She could be worried about how this will affect Harry and his future, and might try to find a way to reverse the situation if it seems harmful to Harry.
One possible plot could be that the girl is a fellow student at Hogwarts who has fainted during a dangerous situation, like a duel gone wrong in a secret passage. Harry, being the heroic type, uses a spell to wake her up. Then they end up having to work together to get out of the passage before it closes or some other threat arrives.
Obviously, Buu and Cell would be main characters.
The Cullens are very likely to be involved. Edward, of course, would have a huge role as Bella's former love interest. Carlisle, with his knowledge and experience as a vampire, could help Bella adjust to her new life. Alice might use her precognitive abilities to foresee any problems Bella could face. Also, Jacob could be in the story. His reaction to Bella becoming a vampire would be interesting, considering his past relationship with her and his werewolf nature.
Obviously, Harry Potter himself would be a main character. Elrond, who is raising Harry, would also be a central figure. There might also be other elves like Arwen, Elrond's daughter, who could play important roles. Maybe some of Harry's friends from Hogwarts could make appearances in the story, even if it's just in his memories.
I think Dobby could also be a significant character in this fanfic. Since he has connections to both the Malfoys and Harry. He might be the one who gives the Malfoys the idea to rescue Harry or helps in the rescue in some way. Also, Voldemort or his Death Eaters could be important in the background as the threat that Harry needs to be rescued from. Their presence would constantly loom over the story, making the Malfoys' actions more dangerous and significant.
Harry Potter himself could be a main character. He has a history of standing up against injustice, so it's likely he'd be involved in a revolt. Hermione would also be a key figure. Her intelligence and knowledge of the wizarding world's laws would be invaluable in planning and leading a revolt. Ron, with his loyalty and courage, would be right there with them.