One idea could be that Percy Jackson accidentally ends up in New York City during one of his quests and runs into Spider - Man. They could team up to fight a common enemy that has powers related to both Greek mythology and some high - tech experiment gone wrong. For example, a villain who can control water like Percy but also has robotic enhancements like some of Spider - Man's foes.
Another plot could involve a powerful artifact from Greek mythology that has found its way to New York. Both Percy and Spider - Man are after it for different reasons. Percy wants to return it to its rightful place in the demigod world to prevent chaos, while Spider - Man is trying to keep it out of the hands of some local criminals who want to use it for evil purposes. Along the way, they learn to trust each other and combine their unique abilities.
Another plot idea is that there's a magical mishap. A spell gone wrong by a new demigod at Camp Half - Blood causes Percy to be transported into the Spider - Man universe. There, he has to team up with Spider - Man to defeat a common enemy. Percy learns about teamwork in a whole new way and also gets to experience what it's like to be a superhero in a different world. He brings back some new ideas and friendships when he finally gets back to his own world.
Another plot could involve a Pillar Man being reincarnated in the world of Percy Jackson. He could try to use his powers to take over the demigod world, and Percy has to figure out his weaknesses and stop him. This could also involve some interesting interactions between the demigod powers and the Pillar Man's unique abilities. For example, Percy's control over water might be used in unexpected ways against the Pillar Man's strength and immortality.
One idea could be exploring the different Spider - People's home universes in more detail. For example, showing what Miles Morales' daily life in his universe was like before becoming Spider - Man. Another could be a team - up between Miles and an older, more experienced Spider - Person from a different universe to face a new and powerful villain.
Perhaps there's a fanfiction where Spider Man and Spider Gwen accidentally swap powers. They have to learn how to use each other's abilities to fight crime. This would lead to some really funny and also challenging situations as they get used to different ways of web - slinging and sensing danger.
One plot idea could be Percy having to team up with Hera to rescue a group of demigods who have been captured by an ancient monster. Hera, despite her usual aloofness, realizes she needs Percy's unique skills.
One idea could be Percy and his friends getting trapped in a virtual game world that's a twisted version of their own. They have to use their demigod skills to defeat the digital monsters and find a way out.
Maybe Percy is sent on a quest to Atlantis because there are rumors of a traitor among the Atlanteans who plans to side with the Titans. Percy has to navigate the complex political situation in Atlantis and figure out who the traitor is before it's too late. He also has to deal with the Atlantean magic which is different from what he's used to.
One idea could be that Percy discovers a hidden realm within the world of the Wanderer. This realm has its own set of rules and challenges that he has to navigate. Maybe he meets new demigods there who have been lost for centuries.
One idea could be Percy having to make a deal with a minor underworld god to save Annabeth from a new and strange curse that's slowly draining her life force. He has to complete a series of tasks in the underworld that test his loyalty and courage more than ever before.
Well, perhaps the shield was once owned by a powerful demigod from the past. In the fanfiction, Percy starts having strange dreams about this demigod and the shield's true origin. As he investigates, he realizes that the shield holds the key to defeating a new, emerging evil that threatens not just Camp Half - Blood, but the entire world of gods and mortals. So, he has to figure out how to unlock the shield's full potential.