One idea could be that Naruto's immortality is due to some sort of ancient ninja magic that has parallels to the magic in the Harry Potter universe. For example, he could have made a pact with a powerful magical creature in the Naruto world that gives him eternal life, and when he enters the Harry Potter world, he has to figure out how this magic works there. Maybe he tries to find a way to share his immortality with his new friends in Hogwarts, like Harry, Hermione, and Ron. He could also use his ninja skills along with his immortality to protect the wizarding world from new threats that the regular wizards are not equipped to handle.
In some fanfictions, Harry might use his magic skills. For example, he could use spells to protect Naruto from a powerful enemy. Maybe he casts a shield charm to block an attack that Naruto couldn't avoid on his own.
I'm not entirely sure if there is a specific one with that exact premise. However, fanfiction authors are constantly coming up with new and unique concepts. Given the popularity of both Harry Potter and Naruto, it's possible that someone has written a story where Harry Potter is a blacksmith within the context of a Naruto fanfiction. It could be an interesting take on the characters and their worlds, perhaps exploring how Harry's skills as a blacksmith could interact with the ninja world of Naruto.
The magic in Harry Potter could be seen as a different form of chakra. Spells could be chakra - based techniques. For instance, the levitation charm could be a chakra technique that Naruto or other ninjas learn. It could be used in combat or just for everyday tasks like moving heavy objects.
One possible plotline could be Naruto trying to find a way to visit the Harry Potter world. He might search for some kind of magical portal or a powerful spell that can transport him there. Another plotline could be Naruto using the ideas from Harry Potter books to improve his ninja techniques. For example, he could learn about the concept of wandless magic and try to apply it to his chakra control.
It also helps in improving creativity. Reading how other fans interpret and expand on the Naruto and Harry Potter worlds can inspire your own creative thinking. You can pick up new writing styles, ideas for plot twists, and ways to develop characters. Moreover, it can be a great way to find a community. People who write and read fanfiction often form groups where they discuss their favorite stories, share their own works, and bond over their love for these two franchises.
One plotline could be Naruto being a transfer student at Hogwarts. He might struggle to adapt to the magic system while also showing off his ninja skills. Another could be Naruto teaming up with Harry Potter to fight a common enemy that threatens both the ninja world and the wizarding world.
One characteristic is the blend of power systems. You'll see things like magic spells co - existing with ninja jutsu. Another is the unique character interactions, for instance, Hermione might have an interesting conversation with Sakura about their respective skills.
Power and responsibility is also a big theme. In these fanfics, characters from both universes have to deal with their newfound powers and the responsibilities that come with them. For instance, if Naruto has to use magic in Hogwarts, he has to learn to control it and use it for good. And for Harry Potter in the ninja world, he has to adapt to the different rules and ethics regarding power.
One great Naruto and Harry Potter crossover fanfiction could be where Naruto is somehow transported to the wizarding world and meets a Professor Potter. In this kind of story, Naruto might use his ninja skills in Hogwarts, like using his chakra to perform amazing feats that baffle the wizards. He could team up with Professor Potter to fight against dark forces that are threatening both the ninja world and the wizarding world.