Maybe in some fanfictions, Annabeth could be written as betraying Percy's trust. For example, she might side with his enemies or reveal his secrets, which would deeply wound Percy emotionally.
In certain fanfiction, Annabeth could be depicted as falling out of love with Percy very suddenly and in a cruel way. She might start ignoring him or treating him poorly, which would be really hurtful to Percy. He's so in love with her and values their relationship, so this kind of change would cause him great pain.
Annabeth would be very shaken up. After the initial shock, she would assess the situation calmly. If Percy is unconscious, she would try to find a way to wake him up. She might talk to him, recalling their memories together, hoping it would reach him on some level. And she would be very protective of him while he's injured, not allowing any further harm to come to him. She would also feel guilty, thinking that if she were stronger or more careful, Percy wouldn't have had to protect her and get hurt in the first place.
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 reason could be miscommunication. Maybe Annabeth said something without realizing how it would come across to Percy. For example, if she was stressed about a quest and snapped at him when he was just trying to be helpful.
Percy might be a bit flustered and embarrassed. He's protective of his relationship with Annabeth, so having Magnus walk in might make him feel like their privacy has been invaded. He could quickly try to shield Annabeth or just look really shocked.
Well, in many fanfictions, Percy is often shown as being physically protective. For example, he would jump in front of Annabeth if there was any danger, like facing a monster attack. He might also be verbally protective, not allowing others to say mean things about her.
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'd probably be shocked at first. But then her face would light up with joy. After all, she and Percy have been through so much together.
She might be heartbroken at first. She could try to jog Percy's memory by showing him things that were important to them.
It could be an enemy from the underworld. Maybe a powerful demon or a vengeful spirit that has a grudge against her. They might use their dark powers to harm her, like sending a bolt of dark energy her way.
Their relationship in the fanfiction could develop in a more mature way. College is a time of self - discovery, and they would be no exception. Percy might become more confident in his abilities and be more assertive in the relationship. Annabeth could become more empathetic towards Percy's insecurities. They could also start planning for their future together, like thinking about post - college life and how they can continue to fight for the good of the demigod world while also having a normal life. Maybe they even consider starting a demigod training program for future generations on their own.