Another possibility is that there is some sort of personal misunderstanding between them. Maybe Susan Bones accidentally reveals one of Harry's secrets or makes a wrong assumption about him in public, which embarrasses Harry and leads to his hatred. Also, it could be that her family background or family connections play a role. If her family has some past issues with Harry's family or friends, it might fuel Harry's negative feelings towards her.
One reason could be a conflict of interests. If they are competing for the same thing, like a magical artifact or a position in a magical society, and Susan uses underhanded tactics, Harry would hate her.
Well, the Dursleys were extremely cruel to Harry. They locked him in his cupboard under the stairs for a long time. They also tried to prevent him from knowing about his magical heritage, which was a big part of who he was. Harry must have felt a great deal of resentment towards them for suppressing his true self.
One possible reason could be his lingering resentment towards James Potter, Harry's father. Snape and James had a long - standing feud during their school days. Since Harry looks a lot like James, Snape might be transferring his old grudges onto Harry.
One possible reason could be a misunderstanding. Maybe Lupin did something that Harry misinterpreted as betrayal or negligence. For example, if Lupin was forced to keep a secret from Harry for his own safety, but Harry found out in a way that made him feel deceived.
One possible reason could be that fanfiction often takes creative liberties that may distort the complex character of Snape that J.K. Rowling created. Snape has a very intricate backstory and personality in the original series, and fanfiction might simplify or misinterpret it.
One possible reason could be jealousy. Maybe the sister is getting more attention from their parents or at Hogwarts. For example, if she is a star student and Harry feels overshadowed.
In a fanfiction, a possible plot could be that Susan discovers a long - lost magical artifact that has a connection to Harry's past. As they explore this connection, they learn more about each other and the wizarding world. Their marriage could also be a platform for exploring different magical cultures within the wizarding world, as they travel and meet new wizards and witches from all corners of the magical realm.
One possible reason could be that in the fanfiction, her parents might have made a sacrifice that left her alone, and she resents them for not being there for her. Maybe she feels abandoned and that has led to her hatred.
Well, in many fanfictions, Susan Bones might use her knowledge of the wizarding world's lore. Since she comes from an old wizarding family, she could share some secrets that help Harry in his fight against Voldemort. For example, she might know about some hidden magical artifacts or spells that are not well - known.
One possible reason could be the Ministry's corruption. In the original series, we saw some Ministry officials being more concerned with power and image than doing what was right. They often turned a blind eye to real threats like Voldemort's return in the beginning. So in the fanfiction, this corruption might be exacerbated, leading Harry to hate the Ministry.