Perhaps in the fanfic's world, there are changes in their goals or values. If Annabeth starts to pursue something that Percy sees as wrong or against their common cause, he could begin to hate her. For example, if she aligns herself with a group that Percy believes is evil, his feelings towards her could turn negative. Fanfic writers often play with these kinds of character - driven conflicts to create engaging stories.
In certain fanfics, a third party might be involved. For instance, a new character could manipulate Percy into believing that Annabeth has some dark secrets or ulterior motives. This false information could make Percy start to hate her. It's also possible that a past event that was not properly resolved in the fanfic universe resurfaces and Percy blames Annabeth for it, causing hatred to grow.
One reason could be jealousy. Maybe in the fanfic, Annabeth gets more attention or praise for her skills and Percy feels left out or overshadowed, which turns into hatred. Another possibility is that there's a rift caused by their different approaches to solving problems. If Annabeth's logical thinking clashes too much with Percy's more instinctive ways, it could lead to resentment.
It could also be that in the fanfiction, Percy is given a new power or ability that Annabeth sees as a threat. Or perhaps Percy is made to side with someone Annabeth dislikes, causing her to 'hate' him in that fan - created story. This shows how different plot elements in fanfiction can change the dynamics between characters.
Perhaps the fanfiction is set in an alternate universe where something has happened to change Percy's feelings towards Annabeth. For example, if there was a betrayal in the fan - created story that made Percy turn against her.
One reason could be jealousy. If Percy starts paying more attention to the child than to her, she might start to resent the child. It's a common trope in stories where a new addition to a relationship, like a child, can cause jealousy issues.
One possible reason is that their personalities clash. Percy is often portrayed as a more outgoing and confident character, while Nico is more introverted and brooding. In a fanfic, this could lead to misunderstandings and animosity between them. For instance, Percy's bold actions might seem reckless to Nico, causing him to dislike Percy.
It might be that in the fanfiction, Calypso represents something that Percy has come to dislike. Maybe she is associated with a force or an idea that Percy opposes, like a form of confinement if she tries to keep him on the island in a more extreme way than in the original tales.
In fanfiction, the politics and intrigues within Olympus might be depicted in a way that makes Percy disgusted. The backstabbing and power - hungry nature of some of the Olympians could be too much for him to bear, so he hates Olympus.
One possible reason could be jealousy. Maybe she sees Percy getting more attention or praise than her in the fanfic world, and that envy turns into betrayal. Another reason might be a misunderstanding. For example, if there's some misinformation spread about Percy that makes Annabeth believe he's done something really bad.
Another possibility is that Percy made a really stupid mistake that endangered himself or others, and Annabeth, being the more level - headed one in some ways, slapped him to snap him out of his foolishness. For instance, if he rushed into a dangerous situation without a proper plan, Annabeth's slap could be a wake - up call.
One possible reason could be a misunderstanding. Maybe Percy did something that Annabeth misinterpreted, like making a decision during a quest without consulting her first, which made her feel disrespected.
One reason could be that the author wants to create drama. By having Percy ignore Annabeth, it can lead to a lot of tension and conflict in the story, which makes it more interesting for readers. For example, it might be a plot device to introduce a new character who then tries to comfort Annabeth, leading to a love triangle situation.