Perhaps Annabeth made a decision without consulting Percy that put him in danger. In the fanfiction world, this could lead to her feeling guilty and apologizing. For example, if she led their group into a trap because of her over - confidence, she'd realize her mistake and say sorry to Percy.
It could be that she said something hurtful during an argument. In the heat of the moment, she might have lashed out and insulted Percy's background or his past experiences. Later, realizing how wrong she was, she would apologize to him.
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.
Maybe he was hit by some magic or a spell that affected his memory. It could also be due to some sort of trauma he experienced that made his mind block out his memories of Annabeth.
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.
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.
It could be due to a misunderstanding. For example, Percy might have done something that Annabeth misinterpreted as betrayal or insensitivity. This could have led to her feelings changing or fading away in the fanfiction.
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 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.