One idea could be to have Naruto characters in the world of Final Fantasy 15. For example, Naruto could be a guest in Noctis' group. He could use his ninja skills like shadow clones to help in battles against the daemons in Final Fantasy 15. His chakra could be seen as a new form of magic in that world.
Another possibility is a story where the power of the crystals in Final Fantasy 15 has some connection to the tailed beasts in Naruto. Maybe the crystals' energy can be used to either control or enhance the tailed beasts. And characters from both universes team up to protect or fight over these powerful elements.
One idea could be to have Naruto characters in the world of Final Fantasy 10. For example, Naruto could be a Blitzball player, using his speed and agility. Sakura could be a healer, like a White Mage in Final Fantasy 10. They could be on a quest to stop Seymour from achieving his evil plans, with Naruto's Rasengan being a powerful attack against the fiends in Spira.
One idea could be to have the characters from RWBY end up in the world of Final Fantasy 15. For example, Ruby could meet Noctis and they could team up to fight some common enemy. Ruby's speed and scythe - wielding skills could be a great addition to Noctis' combat style.
Perhaps a Final Fantasy character gets transported to our modern world and has to work at a Lululemon store to earn money for their journey back home. They learn about modern fashion and the concept of athleisure, and there could be some comical moments as they try to adapt to this new environment.
One idea could be a crossover where Sephiroth somehow ends up in the wizarding world of Harry Potter. Maybe he's a dark force that Voldemort tries to use for his own gain, but Sephiroth has his own agenda. He could use his powerful magic, which is different from the magic in the Potterverse, to create chaos.
Well, it could be really cool. Picture Naruto in the world of Final Fantasy VII. He might use his ninja skills along with the materia system. For example, he could use a fire materia to enhance his fire - based jutsu. It would be a wild mix of two very different universes.
Another possibility is that Pokemon exist in the Naruto world. Some ninja could have Pokemon as partners instead of traditional ninja animals. For example, Sasuke could have a Dark - type Pokemon like Umbreon that would match his cool and mysterious personality. And the Pokemon battles could be incorporated into the ninja battles, adding a new layer of strategy.
One idea could be a crossover where Naruto characters gain the abilities of Needless characters. For example, Naruto could get the power of Adam Blade's regeneration. It would be interesting to see how he uses it in battle, especially against tough foes like Pain or Madara.
Another concept could be a fusion of their powers. Imagine if Naruto was somehow able to absorb Frieza's power or vice versa. This could create a new and extremely powerful being. The story could explore how this new entity would interact with the two different universes. Would it be a force for good or would the power corrupt it? There could be a lot of internal conflict as the combined Naruto - Frieza entity struggles with its new identity and purpose.
Another possibility is that Godzilla somehow ends up in the Naruto world. The shinobi might initially see it as a great threat, but Naruto could try to communicate with it using his ability to sense emotions. Maybe Godzilla is there because it's being chased by an even greater enemy from its own world, and Naruto and his friends decide to help it.
One idea could be a crossover where Naruto characters are transported to the world of DMC 5. For example, Naruto himself could end up in Red Grave City and team up with Dante to fight demons. His ninja skills like shadow clones and rasengan could be interestingly combined with Dante's devil may cry style combat.