If Naruto met Newgate in a fanfiction, Naruto would likely try to understand Newgate's world view. Naruto is all about protecting his friends and village, while Newgate has his own code among the pirates. They could end up having a philosophical discussion about power, loyalty, and the meaning of family. Naruto might learn about the complex relationships in the pirate world, and Newgate could be intrigued by Naruto's ninja skills.
Naruto would probably be very curious about Nami's world. He might constantly ask her questions about the sea, the different islands, and the pirates. Nami would be initially cautious but then grow to like Naruto's enthusiasm. She could use Naruto's strength to her advantage in dangerous situations, like when facing powerful enemies on the high seas.
One idea could be that the Straw Hats end up in the Naruto world and have to team up with the ninja to fight a common enemy. For example, they might face a powerful demon that can only be defeated with both Devil Fruit powers and ninja jutsu. Another idea is that some of the Naruto characters get Devil Fruits. Like Naruto getting a Logia type fruit that allows him to transform into a powerful energy form, similar to his Nine - Tails chakra mode but with new abilities.
In a fanfiction where Naruto is a fishman in One Piece, Naruto would face new challenges. For example, dealing with the discrimination that some fishmen face in the One Piece world. But he'd also have new opportunities. He could use his fishman physiology to swim faster and deeper, discover hidden treasures, and maybe even find a way to connect the ninja world with the pirate world. His Nine - Tailed Fox chakra might also have some interesting interactions with the strange powers in One Piece.
Luffy and Naruto would be an amazing pairing. They both have a strong sense of justice and are extremely determined. Luffy's carefree nature could balance out Naruto's sometimes - overzealous attitude. Another interesting pairing would be Zoro and Sasuke. They are both powerful swordsmen with a dark past and a drive to become stronger. They could have some epic sword battles and also learn from each other's fighting styles.
One Piece's serial time was longer than Naruto's. One Piece started in 1997 and Naruto started in 2007. Therefore, One Piece's serial time was about 10 years longer than Naruto's.
Well, it could be about the Straw Hats accidentally ending up in the Marvel universe. They meet the Avengers and at first there's some misunderstanding because of their different ways. But then they realize they can work together. Maybe Luffy is fascinated by Thor's hammer and tries to lift it, while Zoro wants to have a sword fight with Captain America's shield.
One common theme is the clash of combat styles. For example, when Zoro crosses over to a world like Naruto's, his swordsmanship clashes with ninjutsu. Another theme is adaptation. Zoro has to adapt to new environments, like if he's in a world with different magic systems or cultures.
The Black Pearl could be a treasure in the One Piece world that somehow ends up in the Naruto world. This could cause chaos as the shinobi are not used to such a valuable and strange object. Pirates from One Piece might then travel to the Naruto world to retrieve it, leading to all sorts of interesting interactions between the two groups.
One possible fanfiction could be about a crossover where characters from Naruto and One Piece encounter a mysterious Black Pearl. Maybe the pirates from One Piece are searching for this powerful pearl which has some sort of chakra - like energy. And the ninjas from Naruto are also interested because it could enhance their jutsu. They end up in a battle for the pearl, but then realize they can work together to understand its true power.