A mentor - like figure could also be a main character. This could be an older student or a teacher who takes Annabeth under their wing. They could offer her advice, help her understand the unwritten rules of the new place, and guide her through difficult situations. For instance, if Annabeth is in a new school with a complex social hierarchy, this mentor could help her find her place within it.
Percy would probably be an important character. He's Annabeth's close friend and love interest. His reaction to Annabeth getting her period could be interesting, like he tries to be supportive but is a bit clumsy at first.
There's Tyson, Percy's cyclops half - brother. In high school fanfiction, he can be really endearing as the big, strong but gentle guy. He might be on the school football team or something similar. And then there's Rachel Elizabeth Dare. She could be the artsy girl in school who has a bit of a crush on Percy and causes some jealousy with Annabeth, adding some romantic tension to the story.
Perhaps the story focuses on Annabeth's journey as the new girl in a magical or fantastical setting. She might discover new powers or secrets within this new place. For example, she could be in a world full of mythical creatures and has to learn to navigate it while being the outsider. She may also form unexpected alliances and face off against antagonists who don't like the new presence in their world.
Grover could be a great addition. He could be the goofy but loyal friend who always gets caught in the middle of Percy and Annabeth's drama. For example, he might accidentally spill some secrets that cause more trouble between them. Another good character could be Clarisse. She could be the school bully who has a grudging respect for Percy and Annabeth but still tries to cause problems for them now and then.
The main characters are Annabeth and Jackson, but depending on the plot of the fanfiction, new characters might be introduced. These could be original characters created by the fanfiction writer, perhaps a mysterious mentor figure who guides Annabeth and Jackson on their journey, or a villain who is specifically after them for some reason.
There could be a friendly teacher. This teacher notices the new girl's struggle to adjust and offers her support and advice. For example, the teacher might give her tips on how to make friends or deal with schoolwork.
Percy might be one. They have a close relationship, and in some fanfictions, he could be more forward with his feelings through flirting.
She could meet normal high school students, like the popular kids or the nerdy ones. Maybe there's a really smart student who becomes her study partner.
Obviously, Naruto and Annabeth are main characters. Naruto as the father figure and Annabeth as his daughter. There might also be other characters from the Naruto universe like Sasuke or Kakashi who could be brought into the story to interact with the characters from the Percy Jackson world, like Percy himself or Grover.
Well, Sally, who has always been there for Percy, providing love and support. And Annabeth, the daughter of Athena, known for her strategic thinking and strong will. In this fanfiction, they are the central figures whose meeting is the focus.