One possible reason could be a miscommunication. Maybe Hermione accidentally reveals a secret of Harry's that he didn't want known, and this causes him to feel betrayed and start to hate her. Another reason could be jealousy. If Hermione gets more attention or praise for her magical abilities than Harry in the fanfic, he might develop feelings of envy and hatred. Or perhaps there's a love triangle situation where Hermione is involved with someone Harry doesn't like, and that causes his hatred.
In such a fanfic, it could be due to a personality clash. Hermione is often very logical and by - the - book, while Harry can be more impulsive. If this difference becomes too much in the fanfic, it could lead to Harry hating her. There might also be a situation where Hermione is wrongly accused of something, but instead of believing her, Harry jumps to conclusions and his initial mistrust turns into hatred. And if Hermione were to make a deal with the enemy in the fanfic for what she believes is a good reason but Harry sees it as a betrayal, that would surely make him hate her.
Well, in a 'Harry Potter hates Hermione' fanfic, it could be that Hermione takes a stance on an important issue that directly opposes Harry's beliefs. For example, if there's a debate about how to deal with a certain dark wizard, and Hermione's approach is too lenient or too harsh in Harry's eyes. Also, it might be that Hermione's over - protectiveness of Harry starts to feel smothering to him, like she's constantly interfering in his decisions, which could lead to his hatred. Additionally, if Hermione is somehow involved in a plot that endangers Harry's loved ones, that would be a strong reason for his hatred.
One possible reason could be a misinterpretation of his character. In the original series, Harry Potter doesn't hate Muggles at all. But in this fanfic, perhaps the author wants to explore a 'what if' scenario where something drastic has happened to make him have such feelings. Maybe he's been betrayed by a Muggle - in the fanfic world, this could be a made - up situation that sours his view on all Muggles.
Perhaps in this fanfic, the Weasleys have some actions that conflict with Harry and Hermione's values. For example, if the Weasleys were to make a deal with a dark wizard for the sake of their family's safety and Harry and Hermione found out. This could lead to a rift and hatred. Also, it could be related to a love triangle situation in a very convoluted way. Maybe one of the Weasleys unknowingly gets in the way of Harry and Hermione's relationship, or vice versa, which causes animosity.
Perhaps in the fanfic, there is a love triangle situation involving Ron. If Harry unknowingly gets in the way of Hermione's relationship with Ron, she could develop hatred towards him. Another aspect could be that Hermione feels Harry is getting all the credit for their group's achievements, while she is doing a lot of the behind - the - scenes work, which makes her resentful.
Well, in 'harry hates hermione fanfiction', it could be that the writer is trying to show how misunderstandings can lead to such extreme emotions. For example, perhaps there was a miscommunication about a spell or a magical event that made Harry wrongly think Hermione had betrayed him. Or it could be a way to explore how different personalities might clash more severely than shown in the original series, like Harry's impulsive nature conflicting more with Hermione's logical thinking.
Maybe in the fanfic, there could be a misunderstanding between them. For example, Ron might have accidentally broken Harry's trust in some way, like revealing a secret of Harry's that he wasn't supposed to.
Maybe in that fanfic, there are misunderstandings between Harry and the Weasleys. For example, they might have had an argument over something like magic use or family values that led Harry to dislike them.
One possible plot could be that Hermione does something that Harry perceives as a great betrayal, like perhaps siding with the Ministry when Harry believes they are corrupt. This could lead to a deep - seated hatred from 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.
It could be that Harry finds out about Dumbledore's secrets regarding the Deathly Hallows. If Harry thinks Dumbledore was more interested in the Hallows for his own purposes rather than for the greater good, it might make him hate Dumbledore.
One possible impact is that it can divide the fandom. Some fans who love the original relationship between Harry and Hermione might be put off by such fanfiction. On the other hand, it can also attract new fans who are interested in seeing this new take on the characters.