Another reason could be jealousy. Suppose Percy was getting a lot of attention and praise for his recent achievements, and Annabeth felt overshadowed. Her jealousy could fester and turn into a desire to undermine Percy, leading to her betrayal. However, this would be a more complex and less noble reason compared to the others.
In some fanfictions, Annabeth might betray Percy for power. Maybe she gets lured by some dark force offering her great power and in order to get it, she has to turn on Percy. It could also be due to a misunderstanding. For example, she might be tricked into believing Percy has done something really bad and as a result, she betrays him without realizing the truth.
Percy would likely feel a great sense of hurt and confusion. He might question his own judgment in trusting Annabeth. He could become more withdrawn and less trusting of others in general.
In this kind of fanfiction, perhaps Annabeth might start acting out of character. She could say things she normally wouldn't. For example, she might be more open about her feelings towards her friends or reveal some secrets she's been keeping.
At first, Percy would likely be angry. He's a fighter, and being betrayed by someone he loves would fuel his rage. He might go after Annabeth to demand an explanation. But as the reality sinks in, he could become very sad and withdrawn. He might isolate himself from his other friends as well, feeling like he can't trust anyone anymore. He would constantly be thinking about what he did wrong to make Annabeth turn on him.
One possibility is that it could lead to Percy's downfall. If Annabeth, who has been his close ally and friend, betrays him, it might shatter his trust not only in her but also in others. He could become more isolated and vulnerable, making it easier for his enemies to target him.
Well, it could be that Annabeth and Percy meet in a different setting than in the original stories. For example, they could meet in a modern city but still have to deal with their demigod issues. They might discover new powers or abilities within themselves as they interact. And there could be some romantic moments as their relationship often has that element in fanfictions.
One reason could be that she's scared. The idea of becoming a mother at that point in her life might be overwhelming, and she might think she can't handle it with Percy. Maybe she wants to protect Percy from the difficulties that come with the pregnancy as well.
In this kind of fanfiction, they might have an adventure together. Maybe they'll face a new monster that they haven't encountered before. For example, a mythical creature from a less - known part of Greek mythology.
Perhaps Percy forgets an important promise he made to Annabeth. In their relationship, promises are significant. If he fails to keep one, like a promise to help her with a project or be at a certain place at a certain time, Annabeth would surely be mad. It could also be that Percy accidentally breaks one of Annabeth's creations or possessions, which she holds dear.
Percy might initially feel a great deal of anger. He's been wronged by those he thought were his friends. But then, with Annabeth by his side, he could start to focus on finding out the truth. He might use his skills, like his combat abilities and strategic thinking, to figure out who or what is behind the betrayal.