Well, Harry is obviously the main character since it's about him disowning himself. But his friends like Ron and Hermione are also likely to be important characters as they are closely related to Harry in the original series and would be affected by his decision.
There might also be new characters introduced. For example, someone who helps Harry adjust to his new situation. Maybe an old wizard who has also cut ties with his family in the past and can give Harry some advice on how to survive and thrive on his own.
The other characters' reactions would vary widely. Ginny would be heartbroken. She might feel that Harry has abandoned not just his identity but also their relationship. Neville would be shocked and would probably feel that Harry has let down the whole school. Some of the Slytherins might be secretly glad, thinking that it removes a threat to their own ambitions. However, many of the younger students who looked up to Harry would be confused and disappointed, as he was a symbol of hope for them. Teachers like McGonagall would try to keep the school together in the face of this chaos, while also hoping that Harry would return.
One possible plot could be that Harry, after years of feeling unappreciated or burdened by his fame in the wizarding world, decides to disown himself. He might leave Hogwarts and the wizarding community behind, perhaps to live as a Muggle. He could change his identity and start a new life, away from the constant danger and expectations that come with being Harry Potter.
Hermione would be a very likely character to support Harry. She's his best friend and is always there for him in the original story. Ron too, as they are a trio. Neville could also step up, as he has his own growth arc and could understand Harry's feeling of being alone to some extent.
Perhaps a key plot point is the reaction of his old friends like Ron and Hermione. They might be shocked and try to convince him to reverse his decision. They could struggle to understand his reasons, which could lead to some complex character dynamics.
Definitely Hermione. She would be the one to encourage Harry to keep going and not let his parents' disowning define him. Neville could also be a great support. He has his own experiences of being underestimated, and he could share his strength with Harry. And Luna. Her unique perspective on life and magic could give Harry new ways to think about his situation, and she would offer him her unwavering friendship.
Hermione could be a main character. She might try to figure out why Harry hates himself and be the one to pull him out of that dark place. Ron could also be there, maybe at first not understanding Harry's self - hatred but later becoming a source of support. Dumbledore could be another key character, as he often has insights into the students' minds and could play a role in helping Harry deal with his self - hatred.
Hermione is often a key character. She might stand by Harry's side, using her intelligence and loyalty to help him through the tough times. She could be the one to encourage him to keep going and not let the disownment break him.
There could also be new characters introduced in the fanfiction. Maybe a female wizard who befriends Harry in his new form and helps him understand the female side of the wizarding world better. Or perhaps a villain who specifically targets Harry because of his unique transformation, seeing it as a weakness to be exploited.
Hermione would most likely be one of the main characters. She's always observant and caring towards Harry. So when she notices something is off with Harry, she would do everything in her power to figure out what's wrong and help him. She might use her extensive knowledge of magic to find a solution to his emotional distress.
Obviously Harry is one of the main characters since his name is in the title. It's also possible that there could be characters related to Ravenclaw, like Luna Lovegood who could be involved in the story about Ravenclaw money. Maybe there are also some original characters created by the fanfic author to help drive the plot forward regarding this money issue.