One idea could be that Naruto, with his immortality, somehow ends up in the One Piece world. He could use his ninja skills like shadow clones to help the Straw Hat Pirates in battles. For example, creating a horde of clones to overwhelm opponents during a big fight on an island. Another plot could involve a character from One Piece learning ninjutsu from Naruto. Maybe Luffy wants to add some new moves to his Gum - Gum attacks and Naruto teaches him how to use chakra to enhance his punches.
There could be a plot where Naruto's immortality is somehow related to a long - lost One Piece mystery. Maybe an ancient poneglyph has information about his immortality and how it can be transferred or used to gain ultimate power. The Straw Hats and Naruto then have to protect this knowledge from falling into the wrong hands while also trying to figure out what it all means for Naruto's future.
One idea could be that Naruto, with his newfound immortality, somehow gets transported to the One Piece world. He could team up with Luffy and his crew. Maybe Naruto's jutsu would be mistaken for some kind of devil fruit power. For example, his shadow clone jutsu could be seen as a really strange form of duplication devil fruit ability. Another plot could involve Naruto helping the Straw Hats fight against a powerful enemy that has powers similar to those of the Akatsuki in Naruto's world. He could use his immortality to outlast the enemy in a long - drawn - out battle and find a weakness.
One idea could be that Naruto, with his immortality, somehow ends up in the One Piece world. He could use his ninja skills to help the Straw Hat Pirates in their adventures. For example, his shadow clone jutsu could be used for various tasks like scouting or distracting enemies during battles.
Another plot could involve Naruto using his Rasengan and other jutsu in the One Piece world. His immortality would allow him to explore the mysteries of the One Piece world more freely. For instance, he might join forces with the Straw Hats to uncover the secrets of the Poneglyphs. Since he can't die, he could take more risks in deciphering the dangerous knowledge within them.
One idea could be that a character from Naruto, like Naruto himself, somehow gets transported to the One Piece world. In this new world, he attracts a harem of various female characters from both Naruto and One Piece universes. They all become intrigued by his unique abilities and his positive attitude.
A possible plot is that there's a powerful treasure in the Naruto world that the Straw Hat Pirates hear about. So they sail there. Once they arrive, they meet Naruto and his team. Together, they have to face a common enemy who wants to use the power of both the One Piece and the ninja world for evil. Naruto can teach Luffy and the others some ninja skills like stealth, while Luffy can show Naruto the value of true friendship among his crew. And maybe Zoro could have a sword - fighting duel with a skilled ninja swordsman.
One idea could be that Naruto and Luffy meet in a strange dimension. Naruto's ninjutsu and Luffy's devil fruit powers could create really cool battle scenes against a common enemy. For example, they might face a powerful being who can control time, and Naruto's shadow clone jutsu combined with Luffy's stretching ability would be used in creative ways to defeat it.
One idea could be that Luffy and his crew end up in the Naruto world. They meet Naruto and his friends, and together they have to face a new common enemy. Maybe an Akatsuki member teams up with a powerful pirate from One Piece's world to try and take over both realms.
One idea could be that Naruto and Luffy's crews end up on a strange island. There, they meet a group of powerful and alluring female characters. The females have unique powers related to both the Naruto and One Piece universes. For example, some can use chakra and also have Devil Fruit abilities. The two crews have to team up with these women to face a common enemy, and during their adventures, romantic relationships start to form in this harem - like situation.
One idea could be that the Straw Hats end up in the Naruto world somehow. Maybe Luffy and Naruto meet and instantly become friends because of their similar positive and determined personalities. They could team up to fight a common enemy like Akainu who has somehow also entered the Naruto world and is causing chaos. Another plot could be that the Devil Fruits from One Piece start to appear in the Naruto world, and ninja start to use them in combination with their jutsu, creating new and powerful abilities.
A plot idea could be that the Akatsuki from Naruto somehow cross over to the One Piece world. They all have EMS or Rinnegan powers. They start causing chaos by trying to collect powerful Devil Fruits instead of Tailed Beasts. The Straw Hat crew has to team up with some Naruto characters who also end up in the One Piece world to stop the Akatsuki. It would be a battle of different powers and ideologies.