In fanfiction, if Percy Jackson goes to the Naruto universe, he'd probably be really confused at first. The chakra system would be so different from his demigod powers. But he could learn about it. And his ability to control water could be seen as a really unique jutsu. He might even be mistaken for a very powerful water - style ninja at first. He could also introduce the idea of Greek gods to the Naruto characters, which would be a really wild concept for them.
If Percy Jackson enters the Naruto universe in fanfiction, there are a lot of possibilities. His demigod strength and speed could give him an edge in combat. He might have to adapt his fighting style though. For example, he's used to fighting monsters, but in Naruto, he'd be facing ninjas with different abilities. Also, his relationship with the Greek gods could be an interesting contrast to the ninja world's beliefs. He could potentially find a way to combine his powers with chakra, creating some really unique and powerful attacks.
In this fanfiction, Percy might encounter different versions of his friends. For example, Annabeth could be a powerful sorceress instead of a strategist. He could also face new and strange monsters that are unique to that universe.
If Percy Jackson goes to UA, there would be a huge culture clash at first. The UA students are used to a very structured hero training system, while Percy is more of a 'go with the flow' kind of demigod. But over time, he could teach them about improvisation in battle and they could teach him about teamwork in a more organized way. He might also introduce the concept of Greek mythology to the UA world, which could open up new ways of thinking about powers and abilities.
Well, he might get into all sorts of adventures. He could meet the dragons in Alagaesia and try to use his water powers to his advantage against them. Maybe he'd team up with the local heroes there and learn new combat styles.
Perhaps Percy would see a future where the monsters have evolved in strange ways. They could be more intelligent and organized, posing an even greater threat to the demigods. He might also find that some of his old friends have made great sacrifices and that he has a new role to play in this future world, like being a mentor to the new generation of demigods.
In this fanfiction, Percy might decide to break away from Camp Half - Blood. He could start exploring the mortal world on his own terms, using his demigod powers in ways that the camp rules don't allow. Maybe he teams up with some unexpected allies, like a group of outcast demigods or even some friendly monsters.
In this fanfiction, perhaps Percy will make new friends at Goode who end up getting involved in his demigod world. There could be a plot where the school is in danger, and Percy has to use his powers and knowledge of the mythological world to protect it. Maybe he'll also have some interesting interactions with his teachers who suspect there's something different about him.
Perhaps in this fanfiction, Percy goes to Australia to find a hidden artifact that is crucial for the safety of the demigod world. Along the way, he teams up with local demigods (if there are any in the fan - created story). He would have to adapt to the Australian culture and environment, which is very different from what he's used to in the US. He might also face some new types of monsters that are native to Australia.
In a fanfiction where Percy Jackson goes to Forks, he might be really confused by the gloomy weather. He's used to more sunny and open places. He could meet the Cullens and there would be a clash of his demigod powers and their vampire abilities. Maybe he'd mistake them for some new kind of monster at first.
Well, he might meet Elsa and be really amazed by her ice powers. Since Percy is used to dealing with all kinds of magic in his own world, he could either help Elsa control her powers better or get into some trouble because of the different nature of the magic in Arendelle. Maybe he'd also team up with Anna to fight against some new threat that emerges in Arendelle.
Percy going to Ilvermorny would be a wild ride. First, he'd be amazed by the castle itself. The four houses would be a new concept for him. He might be sorted into a house based on his heroic nature, like Thunderbird perhaps. He'd introduce the idea of Greek gods to the students there, which would cause quite a stir. And his relationship with Annabeth would be put to the test as they are separated by different magical institutions.