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.
In a 'Percy Jackson and Avengers crossover fanfic', the plot could be centered around a prophecy. There's a prophecy in the Percy Jackson world that mentions heroes from another realm (the Avengers). Percy and his friends start having strange dreams about the Avengers. Meanwhile, the Avengers are dealing with a new threat that seems to have some connection to Greek mythology. They cross paths and realize that the only way to defeat this threat is by combining their powers. Thor, being from a mythological background himself, helps bridge the gap between the two groups at first, and they embark on an adventure to save both their worlds.
A plot might involve Loki getting his hands on a powerful artifact from the Percy Jackson world. This causes chaos as it starts to affect the balance of power in both universes. The Avengers, not understanding the magic of this new object, call for help. Percy and Annabeth show up. They have to quickly educate the Avengers about the magical world while also trying to figure out how to stop Loki from using the artifact to take over both their worlds. Eventually, they all team up with their unique skills - the Avengers' tech and combat abilities, and the demigods' magic and fighting skills.
The plot could involve Percy Jackson's world of Greek gods colliding with the Avengers' universe. Maybe the gods have some sort of issue that only the Avengers' powers can help with, or vice versa. For example, an ancient Greek monster has been unleashed in the modern world that the Avengers are struggling to defeat, and Percy and his friends come in with their knowledge of Greek mythology to assist. It could also be a situation where the Avengers are dealing with a threat that has its roots in Greek magic, and they need Percy's demigod powers to counter it.
One possible plot could be that the Greek gods, noticing the powerful threats the Avengers face, send Percy Jackson and his friends to help. Percy could use his water powers to assist in putting out fires during a battle like the one in New York. Meanwhile, Thor could be intrigued by Percy's connection to Poseidon and they could exchange stories about their godly fathers.
One possible plot could be that the Avengers are facing a powerful new threat that has some connection to the Greek mythology world. Percy Jackson and his friends are called in to help. Maybe it's a villain who has the power to control both technology like the Avengers are used to dealing with and also the elements of Greek magic. They would have to combine their skills, with Percy using his water - controlling abilities and the Avengers using their high - tech weapons and superpowers to defeat the villain.
One way could be to have Percy Jackson's powers of being a demigod interact with the superpowers of the Avengers. For example, his ability to control water could be used in a joint mission with Thor's lightning powers. Maybe they are facing a common enemy that can only be defeated by combining their unique skills.
One plot idea could be that Percy Jackson discovers a magical artifact that somehow links his world to the Marvel Universe. Thor senses the power of this artifact and comes to investigate, leading to a meeting with Percy. Meanwhile, the Avengers also get wind of it and think it could be a threat. So, they all end up in a big showdown where they have to figure out if they're on the same side or not.
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.
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.
Another idea is that the Ten Tails' power has some sort of connection to the Greek gods in the Percy Jackson world. Maybe it was once a creation of the gods or has some ancient link. Naruto, being the host of the Ten Tails, is drawn to the Percy Jackson world to uncover this mystery. Percy helps Naruto navigate this new world while also trying to figure out if this new arrival is going to cause chaos or bring a new form of balance.
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 possible plot could be that the gods in the Percy Jackson universe sense a great threat from another dimension (the Marvel universe). Percy and his friends are sent to team up with the Avengers. Percy's water powers could be useful in fighting villains like Electro. Annabeth's strategic mind would assist in planning battles against foes like Loki. They all have to learn to work together, with Percy and the Avengers initially having some clashes due to their different ways of handling things.