A really cool plot could be that Percy has a new start in a parallel dimension where the roles of the gods are reversed. He has to adapt to this new order while also trying to figure out how to get back to his own dimension. Along the way, he might meet alternate versions of his friends and enemies, which would lead to some really interesting interactions.
One idea could be Percy waking up in a new world where the Greek gods are unknown, and he has to start from scratch to regain his powers and find his friends. He could face new monsters that are a mix of modern and mythological threats.
One plot idea could be that Percy Jackson somehow ends up in the world of 'New Girl' and has to navigate the apartment - sharing and relationship drama while also hiding his demigod powers. For example, he might use his water - controlling abilities in a creative way to solve a plumbing problem in the loft, all while trying not to arouse suspicion.
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.
Imagine a fanfic where Percy has to navigate the New York City traffic while being chased by a pack of hellhounds. He has to use his water - based powers in creative ways, like creating water slides on the streets or using sewer water to slow down the hellhounds. This would be a really action - packed and fun story.
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.
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.
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.