A great plot for a 'Percy Jackson at School' fanfic would be Percy competing in a school - wide competition that is secretly a test by the gods. The tasks in the competition could be related to the skills he has learned in his demigod adventures, like sword - fighting or outsmarting a maze - like obstacle. Also, he could befriend a mortal student who starts to suspect there is something different about Percy and his friends, and Percy has to decide whether to reveal the truth or keep the mortal in the dark.
In a fanfic, perhaps Percy and his friends accidentally stumble upon Medusa's lair while on a quest. But instead of immediately attacking, Medusa offers them a deal. She says she will give them a valuable clue to complete their quest if they help her get revenge on one of the minor gods who wronged her in the past. Percy and his friends then have to decide whether to trust Medusa or not.
Another interesting idea is a high school competition between different cabins. Instead of regular sports, they could have contests like who can best use their godly powers in a non - destructive way. It would be a great way to show off the different abilities of the demigods and also create some friendly rivalries.
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.
One idea could be Percy discovers he has a new ability related to his gills that allows him to communicate with underwater creatures in a more profound way. Maybe he can understand their ancient languages and has to use this new skill to solve an underwater mystery that threatens both the sea world and the surface world.
Perhaps being reborn as a child of Poseidon but with a twist. Instead of having the typical water - based powers, you have the power to communicate with sea creatures in a way that no one else can, like understanding their emotions and memories. Or being reborn as a demigod who has lost their memory but slowly regains it as they go on quests and face challenges, and each recovered memory reveals a crucial part of their past and a new power or ability.
Well, perhaps the succubus is sent by an enemy of the gods to disrupt Percy's relationships with his friends. She starts causing jealousy and strife among them by using her alluring powers. Or maybe she's tied to an ancient prophecy that Percy is involved in, and he has to either defeat her or convert her to the side of good to fulfill the prophecy.
One idea could be that Percy adopts a young demigod who has a very rare and powerful ability. Percy has to teach this new demigod how to control their powers while also protecting them from monsters who are after the new kid because of their potential. Another could be that the adopted demigod is from a different pantheon entirely, which causes some interesting cultural clashes and misunderstandings within the Camp Half - Blood environment.
One idea could be a story where Percy and Herera have to team up to save a group of demigods who are trapped in an ancient, cursed labyrinth. They face various monsters and puzzles along the way.
A really interesting plot would be if there was a prophecy related to the Argo. For example, it might be foretold that the Argo must travel to a certain forbidden place to retrieve an ancient artifact that could either save or destroy the demigod world. And the crew has to decide whether to trust the prophecy and embark on this dangerous journey. There could also be a plot where some of the crew members start having strange dreams that seem to be leading them to a hidden mystery related to the Argo's origin.
One plot idea could be Gaea's redemption. In the original series, she was a major villain, but in a fanfic, she could be given a chance at redemption. Maybe Percy and his friends discover that Gaea was being controlled by a more powerful and malevolent force all along, and they have to work with her to defeat this greater evil.