A possible plot is that Voldemort discovers the existence of the demigods and tries to use their powers for his own evil purposes. He sends his Death Eaters to capture some demigods. Percy and his friends manage to escape and seek refuge at Hogwarts. At Hogwarts, they learn about magic in a whole new way while also teaching the wizards and witches about their own powers. The two groups then have to combine their skills, like the demigods' combat abilities and the wizards' spell - casting, to fight against Voldemort and his new - found allies from the world of Greek mythology.
One interesting plot could be that the magical worlds of Hogwarts and Camp Half - Blood somehow merge. Harry Potter and his friends find themselves in the world of Percy Jackson, facing off against mythological creatures they've never seen before. Maybe they have to work together to stop a common enemy that threatens both their worlds, like an ancient dark magic that is starting to corrupt the gods and the wizards alike.
One idea could be that the wizarding world discovers the existence of demigods. Harry and his friends team up with Percy and his crew to fight a common enemy that threatens both their worlds, like an ancient, powerful dark force that feeds on magic and the power of the gods. For example, a new kind of dark wizard who has made a pact with a minor, evil god.
One possible interesting plot could be that the magic from the Harry Potter world starts to seep into the Percy Jackson universe, causing chaos among the demigods. For example, Hogwarts could suddenly appear in the middle of Camp Half - Blood. The demigods, not used to this type of magic, would be both curious and threatened. Meanwhile, Harry and his friends could get accidentally transported to the Percy Jackson world and have to team up with the demigods to figure out how to send Hogwarts back and restore the balance between the two magical systems.
One possible plot could be that Percy and his demigod friends are somehow transported to the Halo universe. They could team up with the Spartans to fight a common enemy, like a new kind of powerful monster that has emerged in the Halo world due to some strange rift between the two universes. Percy could use his water powers in unique ways, for example, to short - circuit some of the Covenant technology which might be vulnerable to water in this crossover scenario.
In a 'Percy Jackson adopts Harry Potter' fanfic, the plot could start with Percy being on some kind of mission that crosses into the wizarding world. He stumbles upon Harry, who is alone and vulnerable. Percy decides to adopt Harry because he sees the same kind of determination and courage in Harry that he has. As they journey together, they exchange knowledge. Percy teaches Harry about Greek mythology and combat skills, while Harry shares his knowledge of magic. They form a bond that helps them face threats from both magical and mythological creatures, and they might even team up to fight against a common enemy that is a threat to both their worlds.
One idea could be that the demigods from Percy Jackson's world accidentally stumble into the realm of the Kane Chronicles. Maybe Percy, Annabeth and some of their friends are on a quest near a portal that leads to the Egyptian magical world. Once there, they meet Carter and Sadie Kane. They soon realize that there's a common enemy that is affecting both their worlds, like an ancient evil that was sealed away long ago but is now starting to break free. They have to combine their powers, the Greek magic and the Egyptian magic, to fight it off. For example, Percy's control over water could be used in creative ways in the Egyptian deserts, and the Kane's magic could help the demigods in understanding some new types of magical threats.
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.
Well, one possible plot could be that the gods in the Percy Jackson universe notice some strange energy disruptions caused by the Infinity Stones in the Avengers' world. Percy and his friends are sent to investigate. They meet the Avengers and at first there are misunderstandings, like the Avengers thinking Percy's powers are from some new form of alien technology. But then they realize they need to work together to stop a common enemy, perhaps a new powerful being that is drawn to the combined power of the demigods and the Infinity Stones.
Perhaps in the crossover, the Prototype virus could somehow infect the magical creatures in the Harry Potter universe. This would lead to a crisis where normal spells and magic can't stop the infected creatures. Harry and his friends would have to seek help from Mercer, who understands the virus. Together, they could try to find a way to either cure the infected or contain the spread. Mercer might use his own knowledge of the virus and his powers to fight the infected creatures, while Harry uses his magic skills to protect Mercer from magical attacks.