One idea could be Percy using his unique skills to solve a mystery at school, like a series of strange disappearances in the school basement. Another could be Percy facing a bully who turns out to be a monster in disguise. Or perhaps Percy starting a club at school to teach other students about ancient Greek mythology.
Well, a cool plot for 'percy goes to school fanfiction' might be Percy getting into trouble for accidentally using his powers during a school sport event. Maybe he makes the basketball hoop explode when he throws the ball too hard. Also, he could meet a new student who is actually a demigod too and they have to team up to deal with a threat that's targeting the school. He could also use his knowledge of the underworld to help the school's history teacher with a project on ancient civilizations.
One idea could be Percy trying to hide his demigod powers from his high school classmates while still using them to solve normal high school problems like bullying. Another could be Percy forming a secret club in school for other kids with special abilities. Or maybe Percy getting into a friendly rivalry with the school's star athlete in a non - combat - related sport like track and field.
One idea could be Percy getting involved in the vampire - human drama in Forks. Maybe he discovers the secret of the Cullens and tries to find a way to co - exist with them, given his own experiences with different species in his own world.
One possible plot idea could be Percy encountering unique Alaskan mythical creatures that are different from what he's used to in other places. Maybe he discovers a tribe with a special connection to the gods that he has to help protect.
One idea could be Percy arriving in Beacon Hills and being mistaken for a new supernatural threat. The local pack tries to figure out his powers and intentions. Another could be Percy teaming up with the pack to fight a common enemy that is drawn to the unique energy of Beacon Hills and Percy's own demigod powers. Maybe he also has to adjust to the high school life there while hiding his true identity from most of the students.
A plot could involve a curse that has befallen the school. The classrooms are in chaos, the teachers are acting strange, and it's up to Percy and his gang to figure out which god or monster is behind it. They'd have to search through the school's hidden passages and use their knowledge of Greek mythology to solve the mystery.
A really interesting plot would be if Percy's friends from Camp Half - Blood transfer to Goode High for some reason. They all have to adapt to the mortal school life while also dealing with the threats that follow Percy, like a vengeful demigod from an enemy camp who wants to expose Percy in the middle of his mortal school life.
Maybe in this high school fanfiction, Percy is on the swim team and Calypso is the manager. There's a big competition coming up and they have to work together to make sure the team is ready. Along the way, they develop feelings. Calypso helps Percy deal with his insecurities about the competition, and Percy shows Calypso that there's more to life than just being popular.
One idea could be Percy having to deal with a new bully at middle school who turns out to be a minor monster in disguise. He has to figure out how to expose the bully without revealing his own identity as a demigod to the regular students.
One idea could be a high school talent show where Annabeth and Percy team up for a project that combines Annabeth's strategic mind and Percy's natural athleticism. They could create a unique performance that showcases both their skills and also their growing relationship.
One idea could be a school competition where Percy and Nico have to team up against other demigods. They could use their unique powers in unexpected ways to win, like Percy using his water control to create cool water sculptures as part of an art contest, and Nico summoning shadowy creatures for a drama performance.