They could have had an adventure in the school library. The library had a restricted section that was said to be haunted. Percy and Annabeth, being the curious ones, decided to check it out. They found an old book that seemed to have some strange power. As they opened it, they felt a gust of wind and strange symbols started to glow. They quickly realized they had to put the book back and figure out how to seal the power within it later.
There was a time when their high school organized a camping trip. Percy and Annabeth were in the same group. In the middle of the night, they heard strange noises coming from the forest. They went to check it out and found a group of small, imp - like creatures causing trouble. Percy used his water powers to create a distraction while Annabeth used her knowledge of the forest and its creatures to find a way to send the imps back to where they came from.
They could be involved in a high school project that turns out to be related to an ancient prophecy. Percy might use his water - controlling abilities in a science experiment in a really cool and unexpected way, and Annabeth would be there to explain the historical context behind it all.
There could be a secret passageway in the school that leads to an ancient mythological place. Percy and Annabeth discover it by accident. Percy is excited to explore but Annabeth warns him to be cautious. They enter together, facing various traps and puzzles inside. Along the way, they might meet some minor gods or spirits who are either helpful or try to hinder their progress. This adventure would test their skills and teamwork, just like their quests in the original stories.
They could have an adventure where they have to retrieve a lost artifact that is important to both their parents. Percy could use his ability to control water to navigate through underwater caves or obstacles, while Annabeth's knowledge of architecture and strategy would help them figure out the puzzles and traps along the way.
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.
One possible fanfic could be about Percy and Annabeth facing a new mystery in high school. Maybe there's a strange teacher who seems to know more about their demigod past than they're comfortable with. Percy could be struggling with his ADHD in the academic setting, and Annabeth is constantly helping him study while also trying to solve the mystery of the teacher.
One idea could be that Percy and Annabeth are new students at a high school filled with mythological secrets. They have to hide their demigod status while also dealing with normal high school problems like exams and bullies. Maybe they join the school's swim team and debate club respectively, which could lead to some interesting interactions.
They could participate in a school sports event. Percy, with his natural athleticism, would be great at swimming or track. Annabeth might be more into something like debate team or chess club. But then a rival school turns out to have some sort of demigod - related threat, and they have to work together to overcome it while still trying to win the sports event or the club competition.
They could have an adventure in the school library. They might discover a hidden section that leads to a magical place. Inuyasha's strength and Kagome's wits would be useful in exploring this new place.
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.
One idea could be that they compete in various school competitions like academic decathlon or sports events, always trying to outdo each other. For example, in a science fair, Percy might do a project on underwater ecosystems because of his love for the water, while Annabeth does something related to architecture. Their rivalry makes them both push harder and come up with more creative ideas.