There might be a character who serves as a sort of antagonist in relation to Sasukw's secret. Maybe someone who is trying to find out the truth about her for their own reasons, whether it's out of jealousy or just a nosy nature. This character would add conflict to the story. And of course, there could be a love interest, someone who Sasukw has feelings for but can't fully express because of her hidden identity.
One possible interesting plot point could be the challenges Sasukw faces in maintaining the secret. For example, she might have to constantly be on guard around certain characters who could potentially expose her.
Obviously, Harry Potter is the main character as it's about him hiding his power. His friends, like Hermione Granger and Ron Weasley, are also likely to be main characters. They might be in the dark about his hidden power at first, which could create some interesting dynamics in their relationships.
The main character is Merlin, of course. He is the focus as he is the one with the hidden pain. Arthur Pendragon is a key figure too. Since Merlin is Arthur's manservant, Arthur's actions, words, or even his ignorance of Merlin's true self can be sources of Merlin's pain. Sometimes, the Great Dragon can also be involved. The dragon might be aware of Merlin's pain and offer some cryptic advice that Merlin has to decipher while still hiding his pain from others.
Since I don't know the exact details of the novel, it's hard to say for sure. But it's likely to have the reincarnated great saint as one of the main characters. There may also be characters who are either helping or hindering the saint in their hidden state.
Obviously, Kaneki as a girl would be one of the main characters. Depending on the plot, other characters from the original story like Touka might also play important roles. They could have different relationships with Kaneki now that she's a girl. For instance, their friendship or rivalry might change in unexpected ways.
Well, the blueberry girl herself is obviously a main character. She's usually the center of the story with her unique traits. There might also be a sidekick, like a little talking animal that accompanies her on her adventures.
Without having read the 'bastards girl fanfiction', we can only guess. The main character is likely the girl who is identified as a 'bastard'. She may be accompanied by a cast of other characters. There could be a group of outcasts like her who form a kind of surrogate family. There might also be antagonists, perhaps those who uphold the social norms that marginalize her. And then there could be characters who are initially indifferent to her but later become important in her journey, like a kind - hearted noble who starts to see her worth beyond her 'bastard' status.
Since it's named 'the sunlight girl fanfiction', the girl herself is bound to be a main character. There could also be other characters like her friends or family members who support her or are part of her journey. Maybe there's an antagonist as well, someone who is opposed to her because of her sunlight - like qualities, perhaps someone representing darkness or jealousy.
Obviously, Fireheart as a girl would be the main character. She would be the center of the story, with her actions and decisions driving the plot forward.
I don't know for sure as I haven't read it. But most likely there is the player himself who is the central character. There might also be friends or foes he interacts with who play important roles in either trying to uncover his past or helping him keep it hidden.