It could be that the author of the fanfic has created a rivalry between them. In some fanfics, authors like to add tension and conflict, and Jason hating Percy could be part of that. Maybe Percy got more attention or praise in the story, and Jason, being a proud character, resents that.
There might be some personal issues between them in the fanfic's universe. Perhaps Percy accidentally offended Jason's family or friends, or there was some misunderstanding that was never properly resolved. This could have festered and turned into hatred on Jason's part.
Jason Grace may have had some bad experiences with Percy Jackson fanfics. For example, he might have read some that were really poorly written, with inconsistent plots or offensive content. This could have led him to form a general dislike for all Percy Jackson fanfics.
Well, perhaps in fanfiction, their characters are often misrepresented. Maybe Percy's personality traits are distorted in a way that makes him seem out of character when paired with Jason, which could lead to Percy seeming to 'hate' Jason in those stories.
Maybe he doesn't like the way some fanfiction portrays Percy or their relationship. Fanfiction can often deviate from the original characters' personalities, and Jason might be a purist who prefers the official versions.
Well, it could be that he values the original story so much that any deviation in fanfiction annoys him. He might feel that the fan - made stories distort the essence of what he experienced in the official Percy Jackson narrative. For example, if fanfiction changes the relationships between characters in a way he doesn't like, it could lead to his dislike.
Maybe in some fanfics, the author wants to create a new and controversial plot. They might make Percy hate Annabeth due to some misunderstandings, like a miscommunication about a quest or Percy believing Annabeth has betrayed him in some way.
Maybe in the fanfic, Percy has some actions or characteristics that Nico doesn't like. For example, Percy might be too self - centered in the story, which goes against Nico's values. Or perhaps Percy has something that Nico desires, like more popularity or a closer relationship with a certain character, and that envy turns into hatred in the context of the fanfic.
Maybe Nico has his own view of the characters. He might think that the 'nicecery' in the fanfic distorts the real relationship or personalities of the characters, so he hates it.
Maybe Frederick has a different view of the original work and thinks fanfiction distorts it. For example, if he is a purist who loves the original Percy story as it is, any fan - made alterations in the fanfiction might be off - putting to him.
Well, it could be that in the fanfiction, Zeus's actions towards Percy's friends or family were not good. For example, if Zeus endangered them or was overly harsh. Percy is a character who values loyalty and justice, so he would hate Zeus for acting against those values.
Maybe Percy has had bad experiences related to alcohol in the fanfiction world. For example, he could have seen someone he cares about become a different, worse person because of alcohol. Or perhaps it goes against his values. He might be a character who values self - control and discipline, and alcohol represents the opposite of that.