One possible reason could be that she might be facing some sort of internal conflict. Maybe she has some unresolved issues from her past that resurface and make her feel like she can't be a part of Percy and their daughter's life. It could also be that she feels pressured by some external force, like a new threat in the world of the fanfiction that she believes she has to face alone and in doing so, she has to leave them behind.
Percy is likely to be heartbroken. He may initially be in a state of shock, not being able to believe that Annabeth has left him and their daughter. He might feel angry as well, feeling betrayed by her sudden departure.
Maybe she's scared because the fanfiction portrays Percy in a way that's out of character for him. Like, it might show him being overly aggressive or having strange powers that she doesn't recognize, which makes her feel like she doesn't really know him anymore.
Well, one possible reason could be that Percy made a really stupid decision without consulting Annabeth first. Like, if he went off on a dangerous mission on his own when they were supposed to be a team. Annabeth is a very strategic person and she might feel betrayed or extremely frustrated by such actions.
It could also be due to some sort of magic or mind - control. A powerful enemy might have cast a spell on Annabeth, forcing her to turn against Percy. In this case, it's not really her own will but the result of external manipulation.
One possible reason could be a misunderstanding. Maybe she saw Percy doing something that she misinterpreted as a betrayal of their friendship or their cause. For example, if Percy was seen talking secretly with an enemy, Annabeth might jump to conclusions without knowing the full story.
Love is a big reason. She loves Percy deeply and is afraid of losing him. In the world of the fanfiction, there could be many threats to their relationship, so she holds on tightly.
One possible reason could be her deep love for Percy. She might see his life as more valuable in the grand scheme of things, perhaps because of a prophecy or a mission that only he can complete. So, she chooses to sacrifice herself to ensure his survival.
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 possible reason could be jealousy. Maybe Percy gets more attention or recognition in their fictional world that makes Annabeth envious and thus appear to hate him.
In the fanfiction world, their personalities might be very complementary. Annabeth is intelligent and strategic, while Percy is brave and impulsive. This yin - yang dynamic could lead to a strong attraction, and the want to kiss could be a natural outgrowth of that attraction.