It could be that in the fanfic's plot, the Weasleys have some actions that go against Hermione's principles. Say, they might be involved in some pranks that have negative consequences for Hermione's studies or personal goals, and that's why she hates them.
Perhaps the author of the fanfic wants to create a unique and unexpected storyline. By making Hermione hate the Weasleys, it can add a lot of conflict and drama. Maybe there are some family secrets or past events within the Weasley family that Hermione discovers and which make her have negative feelings towards them. For instance, if she finds out that the Weasleys were somehow involved in something that she considers unethical in the wizarding world's history.
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.
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 reason could be jealousy. Maybe she sees the Weasleys as getting things too easily in the wizarding world compared to her own hard - earned achievements. For example, they have a big family support system that she lacks, and she might envy that.
One possible reason could be a misunderstanding. Maybe there was a miscommunication about something important, like a plan to fight against the Dark Arts. For example, if the Weasleys accidentally left Hermione out of a crucial part of the plan, she might be very angry.
In this fanfiction, perhaps there's some miscommunication. Maybe the Weasleys' boisterous nature is misconstrued by Harry. For example, their large family dynamic might be overwhelming to him at times, which could be a reason for the 'hate' in the fanfic.
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.
One possible reason could be jealousy. Maybe one of the Weasleys develops romantic feelings for Hermione and the others don't approve or also have feelings for her. Another reason might be related to her magical abilities. If Hermione has some unique magic or knowledge that the Weasleys think can benefit them or their family in different ways, they could fight over it. For example, her knowledge of ancient spells could be seen as a great asset.
Well, in the original, Hermione is like family to the Weasleys. But in this fanfic, it completely flips. Their interactions would become tense and full of hostility instead of the warm and friendly ones we know.
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.
It could also be a misunderstanding. Perhaps Karin is misjudged by Sakura in the fanfic. Maybe Karin did something that was misinterpreted as malicious towards Sakura or someone she cares about, leading to the hatred.