A really interesting plot could be Percy being sent on a mission by Chiron to protect a mortal who is unknowingly a key to preventing a major war between the gods. This mortal has some special connection to an ancient prophecy. Percy has to blend into the mortal world, go to school with this person, and keep them safe from both mortal and mythological threats. He would face challenges like dealing with the mortal's family and friends, as well as any mythological creatures that come after the mortal.
Well, perhaps Percy gets involved in a mystery in the mortal world that seems normal at first but is actually related to the Greek gods in some way. For example, an ancient artifact shows up in a local museum and strange things start to happen around it. Percy has to figure out how to stop the chaos it's causing without getting the attention of the mortal authorities. He might also have to team up with some new mortal friends who have a knack for getting into trouble.
A plot idea could be that Percy discovers a hidden underwater civilization that has been in stasis for centuries. This civilization has a powerful weapon that could either save or destroy the world. Percy has to navigate the politics and power struggles within this new society to either obtain the weapon for the good of the world or stop someone else from using it for evil. Also, Percy could lose his memory and end up in a normal human town. He has to rediscover his powers while also protecting the town from a series of mysterious attacks that are actually related to the world of the gods.
One idea could be Percy having to face a new type of magical creature that is a combination of different mythologies. It would test his skills and knowledge in a whole new way.
Another interesting one - shot could be about a mortal who discovers the existence of demigods through a series of strange events. Maybe they start seeing things that others don't, like strange creatures in the shadows. As they dig deeper, they form an unlikely friendship with a demigod who tries to keep them safe while also keeping the demigod world a secret from them as much as possible.
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 plot idea could be Percy and Annabeth starting a new life in a small town. They could face challenges like dealing with normal high school drama while still having their heroic instincts. For example, they might have to stand up to a local bully who is causing trouble for the other students. Another idea is them going on a road trip across the country, exploring different places and having adventures that are more grounded in the mortal world, like getting lost in a big city and having to find their way back using only their wits.
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.