He could become withdrawn. Percy is a sensitive person at heart. So if Annabeth's actions are really hurtful, like if she cheats on him in a fanfic (although it's a very sad scenario), he would likely isolate himself from her and their friends. He might go off on his own to think things through and deal with his pain privately.
He could become withdrawn. Percy might start to distance himself from Annabeth, not wanting to be around her if she's going to be cruel. He might go off on his own and think about what she said, trying to figure out if he did something wrong.
One example could be a story where Annabeth makes a thoughtless comment that deeply wounds Percy's self - esteem. For instance, she might compare him unfavorably to another demigod in terms of battle skills in front of their peers. This could lead to Percy feeling inadequate and hurt.
It could be an exploration of different character interpretations. Some fans might see Annabeth as having flaws that could potentially harm Percy. By writing these fanfictions, they can express their views on how the characters might react in certain situations that lead to Annabeth hurting Percy. It also gives a chance to explore different plotlines that deviate from the usual positive relationship between them.
She might be initially very angry. Annabeth is intelligent and perceptive, so she would likely feel betrayed that Percy thought he could deceive her. For example, if Percy lies about a mission, she could find out the truth later and confront him immediately, demanding an explanation.
She might initially be shocked. Annabeth is a strong character, so she could start by trying to stand up to Percy verbally, asking him why he's being so mean.
Annabeth might be initially in awe of Percy's new godly status. But she would quickly start thinking about how to use this new situation to their advantage. She is practical, so she would likely start planning how they can better protect their friends and the world.
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.
Some fans might be intrigued. They could see it as an interesting exploration of 'what if' scenarios, even if it goes against the grain of the original story. However, a large number of die - hard fans would probably be quite upset as it goes against the strong bond that was built up between the two characters throughout the books.
He could also become withdrawn and depressed. Percy and Annabeth have a very strong bond, and her death would leave a huge void in his life. He might isolate himself from his friends and family, lost in his grief and memories of her.
He would probably be shocked. Percy has always trusted Annabeth, so being stabbed by her would be completely unexpected. He might initially be unable to believe what's happening.