A possible crossover idea is that a powerful villain from the Thor universe, say Loki, decides to use the chaos of the Naruto world to his advantage. Thor and Naruto then have to put their differences aside, as Thor comes from a world of gods and Naruto from a world of ninjas, and combine their strengths to defeat Loki and his new - found allies in the Naruto world.
One plot idea could be Thor landing in the Viking era and being mistaken for a god. The Vikings might try to either worship or challenge him. Another could be a Viking warrior being chosen by Thor to help him on a quest in Asgard. Or perhaps Thor has to team up with a group of Vikings to fight a common enemy like a giant frost monster.
One idea could be that Thor somehow ends up at Hogwarts. Maybe he's on a mission in the wizarding world and his Asgardian magic interacts in strange ways with the magic of Hogwarts. For example, his lightning powers could cause some chaos during a Potions class when it accidentally zaps a cauldron.
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.
The combination of different power systems. Naruto has his chakra - based jutsus and Thor has his godly powers. Seeing how these powers interact is fascinating.
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.