In the 'izuku hates all might fanfiction', it could be that Izuku discovers some dark secret about All Might. For example, if All Might has been using him as a pawn in a larger scheme. This realization would shatter Izuku's previous admiration and turn it into hatred.
Perhaps in the fanfiction, All Might is written as being overly critical of Izuku. Constant negative feedback and high - pressure expectations can make Izuku resent him. Also, it could be that All Might is shown as being responsible for some misfortune in Izuku's life, like getting him into a dangerous situation without proper support.
Sometimes, the source material itself can be a factor. If there are major changes in the official My Hero Academia storyline related to Izuku, it might make the author's original concept for the fanfiction no longer viable. Or perhaps they had planned the fanfiction to be part of a certain arc in the series, and when that arc didn't play out as they expected in the official story, they abandoned their work.
One possible reason could be that he has had bad experiences with teachers who underestimated him. For example, they might have not recognized his potential and discouraged him from pursuing his dreams, which could lead to his hatred.
One reason could be jealousy. Maybe Snape gets jealous of Lily's other relationships or her popularity at Hogwarts. Another could be a fundamental difference in their beliefs or values that grows over time into hatred.
Maybe in that fanfiction, McGonagall has some actions that Harry misinterprets. For example, she might be too strict with him in a way that he can't understand at that moment.
Maybe in that fanfiction, Nami's character is distorted in a way that Luffy, with his straightforward and honest nature, can't stand. For example, if she is portrayed as overly greedy or mean in a way that goes against the essence of her character in the original work.
One reason could be a divergence from the original character traits. In the original story, Hermione and Ron have a complex relationship with love and friendship. Fanfiction that misrepresents Hermione's feelings towards Ron might go against the essence of her character. Maybe the fanfiction portrays her as hating Ron in a way that doesn't fit with her growth and development in the official series.
It could be due to a misunderstanding. In the fanfic, Remus might say or do something that Harry misinterprets as being against him. For example, Remus could be trying to protect Harry but his actions come across as controlling, which would make Harry dislike him and potentially hate him.
Perhaps in the 'harry hates dunbledore fanfiction', Dumbledore is shown as being involved in some sort of secret plot that goes against Harry's values. For example, if Dumbledore was secretly working with the dark side in the fanfiction, Harry would naturally hate him. Also, it could be that Harry has discovered some long - hidden truth about Dumbledore that completely changes his view of him, like a past misdeed that Dumbledore has covered up.
It could be related to their different personalities. Naruto is very outgoing and impulsive, while Kurenai is more calm and reserved. In the fanfiction, their clashing personalities might lead to Naruto developing a dislike for her. Naruto might feel that Kurenai is too strict or unapproachable, which causes him to hate her.
One possible reason could be a simple rivalry over a shared love interest. Maybe they both like Naruto, and Hinata's jealousy towards Sakura because of Naruto's attention to her could be depicted as hatred in fanfiction.