Well, it could also create a really deep connection between them. Since she can hear his thoughts, they might be able to communicate in a whole new way. They could team up more effectively in battles or quests. Annabeth could anticipate Percy's moves and decisions even before he makes them, making them a very powerful duo.
Their relationship could become more intense. With her hearing his thoughts, they'd be more in tune with each other's feelings. It might make their bond stronger as they'd understand each other on a deeper level.
Perhaps in the fanfiction, there are other characters who are jealous of Annabeth's intelligence or skills. So they start spreading rumors or making unfair remarks. Percy defends her because he knows her true worth and capabilities. He would stand up and say things like 'You don't know her like I do. She's always been there for all of us.'
One possible scenario could be that they meet during a training session at Camp Half - Blood. Percy is new and a bit clueless, while Annabeth is already an experienced camper. She might be showing off her skills, and Percy is in awe of her. Then they start talking, and there's an immediate spark of mutual respect and a hint of rivalry too.
One possibility is that they've had a long and tiring adventure. After facing numerous challenges, they find a moment of peace and Annabeth, exhausted, falls asleep on Percy. It could also be a sign of their deep trust in each other. In fanfiction, this might be used to show the closeness of their relationship.
One possible scenario could be that Percy sacrifices himself to save Annabeth from a powerful and deadly monster. Maybe a huge and ancient sea creature that only Percy can hold off long enough for Annabeth to escape, but at the cost of his own life.
One scenario could be that Annabeth accidentally revealed Percy's secret identity to someone he didn't want to know. This could put him in danger and make him furious with her.
One possible scenario is that Annabeth might lie to Percy about something really important. For instance, she could lie about her whereabouts when she's actually meeting someone who is not a friend to Percy. When Percy discovers the truth, he would feel betrayed and hurt.
One possible scenario could be that they are on a long journey and Annabeth is exhausted. Percy offers his lap as a place for her to rest, showing his care for her. Another might be after a difficult battle where Annabeth is drained, and Percy's lap becomes a safe and comfortable place for her to recover.
One possible scenario could be that Percy got injured and Annabeth needs to tend to his wounds on his torso, so she takes his shirt off. For example, he might have been scratched by a monster during a battle, and she has to clean and bandage the wound quickly.
One possible scenario could be that they are on a long journey and there is limited seating space, so Annabeth simply sits on Percy's lap for convenience. Maybe they are on a boat and there are not enough benches.