One idea could be that Percy and Hermione meet during a magical event that crosses over the Greek mythology world and the wizarding world of Harry Potter. They team up to solve a mystery that involves both magic and ancient Greek curses.
Perhaps they are both summoned to a special realm where they have to compete in a series of challenges. Along the way, they discover that their different magical abilities complement each other. For example, Percy's control over water and Hermione's vast knowledge of spells can be used in creative ways to overcome obstacles. They also start to develop a friendship that might turn into something more as they face more and more difficult challenges together.
A possible plot could be that there is a threat to both the demigod and wizarding worlds. Percy and Hermione are chosen as representatives from their respective sides to form an alliance. As they work together, they learn about each other's cultures and magic systems. Hermione is fascinated by the Greek gods and Percy is intrigued by the magic of wands. They share their knowledge and skills, and in the process, they fall in love.
One plot idea could be Hermione and Percy teaming up to solve a mystery that spans both the wizarding world and the demigod world. Maybe a magical artifact has been stolen and it has the power to disrupt the balance between the two realms.
One idea could be that they discover their relation during a magical crisis. Maybe a dark force is threatening both the wizarding world and the demigod world, and their combined powers as siblings help save the day. For example, Hermione's magic and knowledge of spells combined with Percy's control over water and his demigod strength.
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.
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.