Well, you could start by thinking about the two universes you want to cross. For example, if it's Percy Jackson and Star Wars. Maybe Percy gets transported to the Star Wars universe. He could use his powers in unique ways, like using water manipulation to deal with the desert planets. His demigod abilities would be seen as a strange and new force in that galaxy.
For a Percy Jackson and Doctor Who crossover, the Doctor could accidentally land in the Percy Jackson universe. Percy then joins the Doctor on his TARDIS adventures. They could visit different time periods and places related to Greek mythology in different timelines. Percy would have to adapt his demigod powers to the various situations they encounter, and the Doctor would be fascinated by the existence of demigods.
A unique plot could involve a prophecy that links Percy Jackson and a character from 'Rough Lemon'. The two have to team up to fulfill the prophecy. Along the way, they face many obstacles. They have to learn about each other's cultures and powers. Percy has to teach the 'Rough Lemon' character about the Greek gods, and the 'Rough Lemon' character teaches Percy about the magic of their world.
You could start with a mystery. For example, Nephilim artifacts start showing up in the Percy Jackson world. Percy and his friends suspect foul play and begin to investigate. As they dig deeper, they discover a connection to the Nephilim. This leads to a journey into the Nephilim realm where they must navigate different rules and powers.
You can start by combining different traits of existing monsters. For example, create a character that is part minotaur and part mermaid. This hybrid would have the strength of a minotaur and the aquatic abilities of a mermaid. It could have a unique backstory like being an outcast from both minotaur and mermaid communities.
One way is to make their tattoos a part of their backstory. Maybe a character has a tattoo that was given to them by a mythical creature they once saved. The tattoo has a special bond with that creature, and it gives the character an advantage in certain situations. For instance, if the tattoo was from a centaur, it could give the character enhanced speed and archery skills when they touch the tattoo. This kind of unique connection to their tattoo helps create a distinct character in the Percy Jackson fanfiction world.
You could create a character who is a descendant of an ancient being associated with the Styx. For example, a half - human, half - river spirit. This character could have unique abilities like being able to manipulate the waters of the Styx in ways that Percy can't. They could also have knowledge of the river's deepest secrets, which would be useful in the story.
One idea could be that Naruto, with his powerful chakra and skills, is somehow transported to the world of Percy Jackson. He might be mistaken for a demigod because of his extraordinary abilities. Naruto could then team up with Percy to fight against a common enemy, like an ancient monster that threatens both their worlds.
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 uniqueness lies in the blend of cultures and power systems. Percy comes from a Western - inspired mythological background, and shinobi are from an Asian - inspired concept. When combined with Percy being godlike, it allows for a crossover that can explore how different magic and fighting styles interact. His godlike abilities can introduce new elements to the shinobi world, like the power to control natural forces on a large scale, which could change the balance of power among the shinobi clans. This creates a rich tapestry of storylines that are not found in either of the original universes on their own.
Naruto would be very friendly and eager to make friends, so he'd probably start by introducing himself to Percy and his friends in a very enthusiastic way. Percy might be a bit cautious at first, but as he sees Naruto's powers, he'd be intrigued. They'd start sharing stories about their respective worlds, like Naruto talking about his village and Percy about Camp Half - Blood.
The most interesting plot could be a tournament - style competition. The demigods from Percy Jackson's world and the ninja from Naruto's world are pitted against each other in a series of challenges. Naruto, as a godlike figure, represents the ninja side. The challenges could include things like fighting mythical beasts, solving magical puzzles, and combat against each other. This would force both sides to learn about the other's strengths and weaknesses and could lead to some unlikely alliances.