Well, it could lead to a misunderstanding. Annabeth might think Percy was being inappropriate on purpose, even if it was an accident. Percy would then have to work hard to prove his innocence. He might do things like give her space and apologize sincerely until she forgives him.
One possible plot could be extreme embarrassment for both. Percy might quickly turn away and then there could be a lot of awkwardness between them for a while. They would probably have to have a conversation about boundaries and respect.
In a more comical take, Percy could be so shocked that he slips and falls while trying to back out of the bathroom. Annabeth, after the initial shock and anger, might find it a bit funny too. This incident could then be a running joke between them in the fanfiction, with Percy always getting teased about it by their friends.
She would likely be furious at first. After all, it's a huge invasion of privacy.
One possibility is that it could lead to some awkwardness between them for a while. They might avoid each other's eyes and have stilted conversations until they finally talk about what happened and clear the air.
She might be initially shocked. After all, seeing someone's abs unexpectedly can be a bit of a surprise.
One alternative could be fanfiction about their adventures together. For example, they could be exploring a new and mysterious realm, facing challenges and relying on each other's skills and friendship. Another option is writing about their character growth, like how Percy becomes more confident in his leadership skills and Annabeth in her wisdom, and how they support each other in these aspects.
It could be that he's lost someone important. Percy has had many friends and family in his life, and if he loses one of them, it would be a huge blow.
In this fanfiction scenario, when Annabeth sees Percy on the field trip, it could be a moment full of unspoken emotions. She might be initially hesitant to approach him, but her curiosity gets the better of her. Once they start talking, they could discover that they are both there for a very similar reason related to their demigod world, like looking for a hidden artifact in the location of the field trip.
One possibility is that Annabeth challenges Percy to a little competition related to the field trip. For example, if they are at a museum, they could see who can find the most interesting historical fact about an exhibit first. This would be a fun and friendly way for them to interact and also show off their knowledge.
One reason could be Percy feeling overwhelmed by the challenges he faces. He often has to deal with dangerous quests and the weight of the world on his shoulders. When Annabeth sees him cry, it might be because he's finally letting out the stress and fear that he's been holding in. For example, in some fanfictions, after a particularly difficult battle where he loses a friend, Percy breaks down in front of Annabeth.
One possible plot could be about their journey of preparing for the baby. Percy might be worried about protecting his family from the various threats in their world, while Annabeth could be focused on creating a stable home environment. They'd also have to deal with the reactions of their friends like Grover and the other demigods.
One possible plot could be Percy and Annabeth adjusting to college life while also dealing with new mythological threats. Maybe they have to take on a monster that is hiding in the college library, using their demigod skills and the knowledge they gain from their classes.