It might also be related to some sort of enemy or threat that specifically targets Percy and his relationship with Annabeth. The enemy could be so powerful that Percy realizes the only way to stop it from harming Annabeth is to sacrifice himself, like if the enemy feeds on his life force or his connection to Annabeth, and he chooses to end it by sacrificing his own life.
One possible reason could be her deep love for Percy. She might see his life as more valuable in the grand scheme of things, perhaps because of a prophecy or a mission that only he can complete. So, she chooses to sacrifice herself to ensure his survival.
Maybe he faced an extremely powerful enemy that he couldn't overcome. It could be a new and terrifying monster created by the Titans or some other dark force.
On the other hand, she could try to honor Percy's sacrifice. Annabeth might focus on the reasons why Percy died for her and strive to fulfill any tasks or goals that he might have hoped she would achieve. She would carry on his legacy in a positive way, even though she is heartbroken.
Well, if Annabeth dies in a fanfic, it would be a really tragic turn. Percy would be completely devastated. He's been through so much with her, and she's not just his girlfriend but also his partner in all their adventures. Their relationship has been a central part of the Percy Jackson series, so her death would change the whole dynamic. Fans would be heartbroken too, as Annabeth is a very popular character. It could lead to Percy going on a dark path, seeking revenge or just shutting down completely.
Well, it would probably shatter Annabeth. Percy is her closest friend and love. His death would leave a huge void in her life. She might become more withdrawn, consumed by grief. She could also become more determined to carry on Percy's legacy in the fight against the forces they were up against.
Well, one possible reason could be that Percy made a really stupid decision without consulting Annabeth first. Like, if he went off on a dangerous mission on his own when they were supposed to be a team. Annabeth is a very strategic person and she might feel betrayed or extremely frustrated by such actions.
It could also be due to some sort of magic or mind - control. A powerful enemy might have cast a spell on Annabeth, forcing her to turn against Percy. In this case, it's not really her own will but the result of external manipulation.
Percy would be completely devastated. He might go into a state of shock at first, unable to believe that Annabeth is really gone. Then he could become filled with rage, vowing to take revenge on whoever or whatever was responsible for her death.
One possible storyline could be that in a battle against a new and powerful enemy, Annabeth sacrifices herself to save Percy. Maybe she steps in front of a deadly attack meant for him, like a powerful magic blast from a primordial being. This would shatter Percy, leading him on a journey of both revenge and self - discovery as he tries to come to terms with her loss.
One scenario could be that they are facing a powerful monster. The monster is about to strike Annabeth, and Percy jumps in front of her at the last moment, taking the fatal blow. Another possibility is that they are in a dangerous situation like a collapsing building or a sinking ship, and Percy uses his powers to ensure Annabeth's escape while he stays behind and perishes.