Perhaps there's a character crossover in a more unique way. A demigod in the Percy Jackson world has a distant relative who was cursed in the Diablo world. This demigod, through some magical accident, gets transported to the Diablo realm. Percy, worried about his friend, follows. In the Diablo world, they have to adapt to the darker and more brutal environment. Percy has to use his skills in a different way, like his water powers to cool down the hellish fires. They meet Diablo - like characters who may not be all bad, and together they try to break the curse and find a way back home.
The demigods from Percy Jackson's world would interact with the Diablo characters in different ways depending on their personalities. Annabeth, being the strategic thinker, would try to analyze the Diablo characters' weaknesses and form plans. She might try to communicate with any intelligent Diablo creatures to find out more about their world. Grover, with his connection to nature, might be really disturbed by the corrupted and dark nature of the Diablo world. He could try to find any remnants of good or nature in that world to help in the fight against the dark forces. And when it comes to the Diablo characters, some of the more cunning ones might try to manipulate the demigods for their own ends.
One possible plot could be that the characters from Avatar find themselves in the world of Percy Jackson. For example, Aang could meet Percy and they discover that their powers, though different, are both related to elements in a way. Aang's airbending and connection to the spirit world might be seen as similar to Percy's connection to the water and his demigod powers. They could team up to fight a common enemy, perhaps a new kind of monster that is threatening both the Avatar world and the demigod world.
One possible plot could be that Percy Jackson, with his demigod powers, somehow gets transported to the world of Overlord. He might initially be seen as a strange being by the denizens of that world. He could team up with some of the characters from Overlord to fight against a common enemy, like a new powerful dark force that threatens both his world and the Overlord world. His water - based powers would be quite unique there and could be used in creative ways during battles, for example, to put out fires in a burning city or to create barriers against enemy attacks.
The plot could involve a villain who has found a way to cross between the two worlds. This villain starts causing chaos in both the world of Percy Jackson, like turning demigods against each other, and in Eragon's world, by disrupting the dragon - rider bond. Percy and Eragon, being the main heroes, have to team up. They start by trying to understand each other's powers and the rules of their respective worlds. Along the way, they make new friends and allies from both worlds and face many challenges together until they finally defeat the villain and restore peace in both their worlds.
A great plot could be that Thanos somehow discovers the power of the Greek gods and tries to steal it for himself. He starts by attacking Camp Half - Blood. The Avengers, who are aware of some strange energy signatures coming from that area, go to investigate. There they meet Percy and his friends. At first, there is mistrust, but they soon realize they need to work together. Percy and his friends help the Avengers understand the magic and powers related to the Greek gods, while the Avengers offer their high - tech weaponry and combat skills. They then embark on a journey to stop Thanos from achieving his goal, facing many challenges along the way, including some Greek monsters and Thanos' minions.
The plot might involve Naruto being mistaken for a demigod at first. Since he has such extraordinary abilities in his own world, in the Percy Jackson world, he could be seen as a very powerful and mysterious figure. He might have to learn about the Greek gods and their ways while also teaching Percy and his friends some of his ninja techniques. And together they'd go on quests, like trying to retrieve a powerful artifact that could potentially destroy both worlds if it fell into the wrong hands.
The plot could start with a strange rift opening between the Naruto universe and the Percy Jackson universe. Naruto, with the Juubi's power inside him, gets sucked into the Percy Jackson world. At first, there's a lot of confusion. The demigods are on guard, thinking Naruto is a new kind of threat. But as they start to communicate, they realize they have a common enemy in the form of a powerful being that wants to take advantage of the chaos caused by the rift. So, they team up to fight this enemy.
One more theme could be the idea of corruption. The Diablo world is known for its corrupting influence. Percy, being a hero from a different world, may have to resist this corruption. This can create internal struggles within him as he tries to stay true to his values while dealing with the dark forces around him. And of course, the theme of adventure is always there. Exploring the unknown regions of the Diablo world, finding treasures, and fighting bosses are all things that make these fanfictions exciting.
Well, it could be that the Voltron team somehow gets transported to the Percy Jackson universe. Maybe they end up at Camp Half - Blood and have to team up with the demigods to fight a common enemy, like a new type of monster that is a combination of a Galra and a Greek mythological beast. The Voltron lions could be seen as some sort of strange new magical creatures by the demigods.
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.