Percy might also start thinking about their relationship while she sleeps. He could be reflecting on all the adventures they've had together and how much she means to him, all the while being careful not to disturb her slumber.
He could be a bit surprised at first, but then a warm feeling would spread through him. He might gently stroke her hair or cover her with a jacket if she seemed cold, all while having a soft smile on his face.
Maybe she had a long day of training or adventuring. She could have been mentally and physically exhausted from dealing with various challenges in their world, like fighting monsters or solving complex puzzles.
Some characters might find it cute. For instance, Grover could just smile to himself seeing how close his friends are. He might even be a bit envious of their relationship.
Percy might feel a deep sense of contentment. He and Annabeth have a special bond, and having her trust him enough to sleep in his lap could make him feel warm and happy inside. He may also feel a bit nervous, not wanting to move and disturb her peaceful slumber.
Annabeth is known for her intelligence and strategic thinking. She is a strong and independent character. Percy, on the other hand, is brave and has a strong connection to the water due to his father being Poseidon. In the fanfic, when Annabeth sits in Percy's lap, it might be a way to show their unique relationship which has developed over the course of their many shared experiences in the Percy Jackson universe.
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.
Annabeth could be shocked at first. She might not have expected Percy to be so straightforward with his feelings. She would need a moment to process what he's said, and then she might respond in a more measured way, like asking him some questions to make sure he's serious.
It could signify trust. Annabeth trusts Percy enough to be in such an intimate physical position. It shows that she feels safe with him.
Annabeth could also be angry, not at Percy but at the situation or the forces that led to his death. She might vow revenge and start on a journey to find out who or what was responsible for Percy's sacrifice and make them pay. This could lead her into a whole new set of adventures and challenges as she tries to come to terms with her loss.
She might be heartbroken at first. She could try to jog Percy's memory by showing him things that were important to them.
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.