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.
Well, perhaps the UNSC discovers a strange energy signature that turns out to be related to the magic in the Percy Jackson universe. They send a team of Spartans to investigate, and they end up meeting Percy and his friends. Together, they have to stop an ancient evil that was sealed away in both universes long ago but is now starting to break free. The Spartans could learn about the power of the gods from Percy, and Percy could learn about advanced technology from the Spartans.
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 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 Master Chief somehow gets transported to Skyrim. He could use his advanced combat skills and high - tech weaponry in the medieval - like setting of Skyrim. For example, facing off against dragons with his energy sword, creating a really cool contrast between the high - tech and the fantasy elements.
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.
Definitely Percy Jackson himself. His ability to control water and his overall demigod powers would make for some really cool interactions in the Halo universe. He could be a bit of an outlier among the Spartans, but his courage and quick thinking would be assets. Also, Master Chief. His stoic and badass nature would contrast well with Percy's more impulsive and humorous side. When they team up, it would be an amazing duo to write about.
Imagine if the gods in the Percy Jackson universe decide to test the mortals in the Kickin It world. They send Percy as a sort of envoy. Percy arrives at the dojo and challenges the students there to a series of tests. At first, the Kickin It gang is angry and confused. But as they engage in these tests, they start to learn about their own hidden potential. Meanwhile, a dark force from the underworld notices this interaction and tries to disrupt it. Percy and the Kickin It gang then have to work together to defeat this dark force. Along the way, they exchange their skills and knowledge, with Percy teaching them about Greek mythology and the Kickin It gang teaching him martial arts moves.
One possible plot could be that the Volturi from Twilight discover the existence of demigods from the Percy Jackson world. They see the demigods as a threat to their vampire supremacy. Percy and his friends have to team up with some of the more friendly vampires, like the Cullens, to fend off the Volturi. This would bring together the magic and powers of both universes in an epic battle.
Well, perhaps there's a villain in the Percy Jackson universe who discovers that the iCarly web show has a huge following and decides to use it as a way to spread chaos. The demigods have to team up with the iCarly crew to stop this. The iCarly gang has to learn about the world of Greek mythology really fast and help the demigods navigate the modern world of technology and media to defeat the villain.
Well, it could start with a magical accident. In the Percy Jackson universe, a spell gone wrong sends Percy, Annabeth, and Grover into the land of Alagaësia from Eragon. There, they discover that the demigod powers Percy has are seen as a strange and new form of magic. Eragon is initially suspicious of them but realizes they can help in his fight against Galbatorix. They combine their skills, Percy's water - controlling powers and sword - fighting skills, along with Annabeth's strategic mind and Grover's nature - sensing abilities, with Eragon's dragon - riding and magic - wielding skills to take on the dark forces.
The plot could involve a powerful magical artifact that has military applications. The NCIS comes across this artifact during an investigation but doesn't understand its true nature. Percy Jackson and his friends, who are on a quest to retrieve the artifact for the demigod world, cross paths with the NCIS. There is a lot of miscommunication at first as the two groups have different goals and ways of operating. But as they realize that they are both facing a common threat from a group of rogue demigods and power - hungry military personnel, they join forces. Percy uses his knowledge of the demigod world and his powers to help the NCIS agents navigate the magical aspects while the agents use their resources and combat training to take on the human threats.