A cool crossover could involve a shared enemy. Some powerful entity that threatens both the Naruto world and the world of Bullet Storm. Naruto and the Bullet Storm protagonists would then have to team up, with Naruto using his sage mode and the Bullet Storm guys using their acrobatic shooting skills to take down the common foe.
Another interesting plot might involve a new and unique jutsu being created by a character. This jutsu could change the power dynamics in battles and force characters to adapt their strategies. It could also lead to a whole new arc of the story where characters are trying to either master this jutsu or find a way to counter it.
One idea could be a Naruto and One Piece crossover. Naruto and Luffy could meet and have to team up to defeat a common enemy that threatens both their worlds. Maybe a powerful dark force that can manipulate the sea and the land.
One idea could be exploring the backstories of the cursed children in more detail. For example, you could write about a cursed child's life before she was paired with a promoter. Another idea is to create an alternate ending to the story, where the situation between the Gastrea and humans is resolved in a different way.
One idea could be that the Ninja Storm Rangers cross over with another ranger team from a different season. They could combine their powers to fight a super - powerful villain that neither team could defeat alone. For example, the combined ninja and ranger powers could create new attack moves and strategies.
Well, one interesting idea could be the combination of Naruto's ninja skills with the powers from another fictional universe. For example, if Naruto were to cross over with the Harry Potter universe, his chakra-based jutsu could interact in unique ways with magic. Maybe he could use his Shadow Clone Jutsu to confuse Death Eaters while wizards try to figure out how to counter it with spells.
One idea could be that Naruto characters are transported to the AOT world. Naruto's ninjutsu skills would be a huge advantage against the Titans. For example, his Shadow Clone Jutsu could be used to distract the Titans while the Survey Corps make their moves. Another idea is that the Ackermans have some sort of connection to the chakra system in Naruto. Maybe they can unlock chakra and use ninjutsu, which would completely change the dynamic in the AOT world.
One idea could be that the characters from Naruto end up in the world of Blade. For example, Naruto himself might be mistaken for a powerful being in the Blade world. He could use his chakra powers in new and unexpected ways against the vampires in that world.
One idea could be Naruto characters attending a modern-day high school. For example, Naruto could be the class clown who always gets into trouble but has a heart of gold. Sasuke might be the mysterious loner that all the girls are curious about. Another idea is a school tournament where Naruto and his friends use their ninja skills in a non - lethal way, like a sports - like competition within the school grounds.
One interesting idea could be Naruto getting the power of flight from another fictional universe. It would completely change his combat style and how he moves around the Hidden Leaf Village. Another idea might be Naruto having the power to control time, like being able to slow down or speed up time during battles. This would give him a huge advantage against his enemies.
Perhaps the Akatsuki from Naruto somehow get involved in the Avatar world's politics. Their goals of collecting tailed beasts could be translated into a search for some powerful Avatar - related artifacts. This would stir up a lot of chaos in the Avatar world and force the Avatar and his friends to team up with some Naruto characters to stop them.