A great plot for a Percy Jackson chat room fanfiction could be a competition organized within the chat room. The demigods compete in challenges that test their skills, like a riddle - solving competition based on Greek mythology, or a virtual battle where they have to strategize using their powers. The winner could get a special prize, like a rare magical item. Or perhaps the chat room is used as a platform for demigods to find partners for a secret mission that requires a combination of different skills, like a son of Poseidon teaming up with a daughter of Athena.
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 to focus on the friendships formed in the locker room. For example, Percy and his friends sharing their adventures and fears while getting ready for a big game or training session. They could talk about their recent battles with monsters and how it affects their confidence in normal activities like sports.
Well, you could have a fanfiction where a new character creates a chat room specifically for Supernatural characters to interact with each other outside of their usual battles. It could be a place where they share their fears and hopes. Maybe Castiel accidentally enters this chat room not knowing what it is and has some really funny exchanges with the other characters. Also, the chat room could be a time - traveling one where characters from different eras of the Supernatural universe can communicate.
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.
Here's an idea. Emma could be a mortal who accidentally stumbles upon the world of demigods. Percy is tasked with protecting her while also trying to keep the secret of the demigod world from getting out. As time passes, Emma shows an uncanny ability to understand the demigod world, almost as if she has some latent demigod blood in her. They develop a bond as they face various monsters and challenges sent by the gods who are not happy with a mortal being so involved. Their relationship could be a mix of friendship and something more as they go through these experiences together.
One interesting plot idea could be a crossover where Percy Jackson's demigod powers interact with the magic in The Originals. For example, his ability to control water could be used in a battle against the vampires in New Orleans. Maybe he helps the Mikaelson family during a flood caused by a powerful witch, using his water - based powers to save them and in turn they help him with some demigod - related problem he has, like finding a lost artifact.