One plot idea could be that Percy and Harry discover they are long - lost brothers and have to combine their magical powers to defeat a new, powerful dark force that threatens both the wizarding world and the world of Greek gods. For example, they might have to find a way to stop a dark wizard who has made a pact with a rogue Greek god to gain ultimate power.
Perhaps they start off not knowing they are brothers. Harry is at Hogwarts and Percy is at Camp Half - Blood. But then strange things start to happen. They both start having visions of the other's world. Eventually, they meet and find out they share the same father. Then they go on a journey to find out more about their family history and in the process, face challenges from both the wizarding and demigod communities who are against their union.
A plot could involve a competition between the two groups. Maybe the wizards challenge the demigods to a series of magical and physical tasks. This would lead to some really interesting interactions as they learn about each other's abilities. The demigods would be amazed by the wizard's spells and the wizards would be in awe of the demigods' powers.
One idea could be that Percy and Triton have to team up to stop an ancient sea monster that is threatening the underwater kingdom. They start off not trusting each other but as they face challenges together, they learn to work as a team.
A plot where the villains from both universes team up. Voldemort and the Titans or Giants could join forces. This would force Percy and Harry to put aside their differences and work together. They would need to combine their unique powers and knowledge. Percy's ability to control water and his combat skills along with Harry's magic skills and knowledge of the wizarding world's secrets would be crucial in fighting this powerful alliance.
Well, they could be the result of some sort of cross - over experiment gone wrong (but in a good fanfic way). Maybe they have powers from both worlds but struggle to control them at first. For example, they might accidentally cast spells while trying to use their demigod powers. And they could be the bridge between the two groups of friends. The demigods are skeptical of wizards and vice versa, but the twins help them understand each other.
One idea could be that Harry and Percy meet during a magical convergence. They realize they can combine their powers to fight a new, powerful dark force that threatens both the wizarding world and the world of the Greek gods. For example, Percy could use his water powers to put out a magical fire created by a dark wizard, while Harry uses his magic to protect Percy from a monster attack.
One idea could be that the twins have powers from both the wizarding world and the demigod world. They can use magic spells like in Harry Potter and also have the abilities of a demigod from Percy Jackson. For example, they can control water like Percy and at the same time cast defensive spells. Another plot could be that they are sent on a mission to stop a threat that endangers both the wizarding world and the Camp Half - Blood. They have to use their combined knowledge and skills to succeed.
One idea could be that the demigods and wizards have to team up to fight a common enemy that is threatening both the magical and the mythological worlds. For example, a dark force that can manipulate both magic and the powers of the gods. Another plot could involve Percy and his friends getting lost in the wizarding world and having to navigate Hogwarts while also dealing with their own demigod issues. Maybe they discover that some of the magic in the wizarding world has its roots in the ancient Greek magic that the demigods are familiar with.
A great plot could involve a prophecy that requires the combined powers of both demigods and wizards. For example, a dark force is rising that can only be defeated if the magic of Hogwarts and the powers of the Olympian gods work together. So, Harry Potter and Percy Jackson have to put aside their differences and form a team. Along the way, they discover that their two worlds have more in common than they thought, like the existence of different types of magic and the importance of loyalty and friendship.
One idea could be that a new character, who is a powerful wizard - demigod hybrid, enters both the wizarding world of Harry Potter and the demigod world of Percy Jackson. This character unknowingly attracts the attention of various characters from both universes, like Hermione, Ginny from Harry Potter and Annabeth, Piper from Percy Jackson, creating a harem - like situation. They all end up teaming up with this new character on different adventures, with some underlying romantic tensions.