It could be that the author has a different interpretation of the characters. They might see some aspects of Ginny that they think Harry would dislike, so they write it that way. For example, if they think Ginny's boldness might be off - putting to Harry in a certain situation.
Sometimes, it's just for the sake of creating conflict. A story with Harry hating Ginny would have a lot of built - in tension and drama, which can make for an interesting read. It allows the writer to explore how the other characters would react to such a rift in their relationship.
Maybe the writer wants to create a unique plot twist. In some fanfics, authors like to deviate from the original relationship to explore different character dynamics.
One consequence could be a split in the friendship group. If Harry hates Ginny, Ron, being Ginny's brother, would be in a difficult position. It could lead to a divide between Harry and Ron as well.
Maybe in the fanfic, Harry has some unresolved personal issues. He could be haunted by his past traumas, like the death of his parents and his battles with Voldemort, which make him feel that he's not in the right mental state to get married.
Well, some fanfic writers might explore such a concept for the sake of creating an alternative storyline. Maybe they want to see how the dynamic between Harry and Hermione would change if there was conflict or hatred, adding a new and unexpected twist to the well - known relationship.
In some fanfics, the idea of Naruto hating Hinata might be a plot device to create drama. Maybe the writer wants to explore a different kind of relationship dynamic than the canon one. It could also be that the writer has a unique interpretation of the characters' personalities and how they might clash in certain situations.
Maybe in the fanfic, the writer wants to create a unique plot where Aang has some misunderstandings about Katara. For example, he might misinterpret her actions or words, leading to dislike.
Maybe the OC has a completely different personality or set of values from what is often portrayed in Rias fanfic. It could be that the OC has had bad experiences related to the typical tropes or themes in those fanfics.
Maybe it's because Aphrodite's powers and the way she uses them are at odds with Naruto's own beliefs. Naruto believes in self - improvement through training and facing challenges head - on. If Aphrodite uses her love - related powers in a way that seems unfair or goes against Naruto's sense of justice in the fanfic, he would dislike her. Like if she uses her powers to manipulate people's emotions for her own gain, which is something Naruto would oppose.
She might hate sonic fanfic because she has her own ideas about how Sonic's story should progress. Fanfics are written by many different people with different interpretations, and perhaps she doesn't agree with the general direction that a lot of fanfics take. Also, some fanfics could be poorly written, which might also contribute to her dislike.
This type of fanfiction can also change the character interactions. Friends of Harry and Ginny may be forced to take sides or try to reconcile them. For instance, Hermione might be in the middle, trying to figure out what went wrong and how to fix it. It can make the story more about relationship drama rather than the typical Harry Potter adventures against dark forces.
Ginny might be overjoyed. She could blush deeply and then give Harry a big hug, telling him she feels the same way.