Well, there could be some jealous classmates too. If there are girls who like Percy, they might not be too happy to see Annabeth. But overall, most of the classmates would probably be friendly and welcoming once they get to know her better. She has that kind of charm that can win people over, even if she seems a bit different at first.
Some of Percy's classmates might be in awe of Annabeth. She's smart and confident, so they could be a bit intimidated at first. But then they start to admire her for her knowledge.
His classmates could be really curious about her. Since she's not from their school, they would want to know all about her. Maybe they ask her a million questions about where she's from and what she likes to do. And when they find out she's into things like architecture and ancient history, they might be really impressed.
It's possible that they have an adventure related to a school project gone wrong. For example, if they are doing a project on Greek mythology and accidentally summon a minor deity or a mythical creature. Then they have to figure out how to send it back without causing chaos in the school and also keep it a secret from the regular students.
Percy would be overjoyed. He's always happy to see Annabeth. He'd probably have a big grin on his face and give her a huge hug right away.
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.
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.
Annabeth's reaction could vary. If she's been missing Percy a great deal, she'll be overjoyed. She might show him around the school, proud to introduce him to her friends or teachers (if possible in the context of the fanfiction). However, if she's in the middle of something important like a test or a big project, she could be a bit annoyed at first but still be happy to see him deep down.
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.
Annabeth could also try to solve the problem that's making Percy cry. If it's related to a quest or a danger, she'll start thinking of ways to fix it. In some fanfictions, she might say 'Don't worry, we'll figure this out together.' and then start making a plan.
At first, Percy would likely be angry. He's a fighter, and being betrayed by someone he loves would fuel his rage. He might go after Annabeth to demand an explanation. But as the reality sinks in, he could become very sad and withdrawn. He might isolate himself from his other friends as well, feeling like he can't trust anyone anymore. He would constantly be thinking about what he did wrong to make Annabeth turn on him.