A cool plot could be that a dark force from Naruto's world has found a way into Moana's world. Naruto, with his knowledge of fighting evil, and Moana, with her knowledge of the local terrain and the ocean, must work together. Naruto might be a bit clumsy at first with the whole sailing thing, but his combat skills are invaluable. Moana, on the other hand, can communicate with the ocean to get them out of tight spots, and together they defeat the dark force.
It could be about Naruto somehow ending up in Moana's world. Maybe he uses his ninja skills to help Moana on her journey to save her island. For example, Naruto could use his shadow clone jutsu to do multiple tasks at once like helping to repair damaged parts of the island while Moana focuses on finding the heart of Te Fiti.
One idea could be a Moana crossover with Frozen. Moana could end up in Arendelle due to a magical storm. She teams up with Elsa and Anna to stop an approaching iceberg that is threatening both her island and Arendelle. Moana's skills in sailing and her connection with the ocean could be combined with Elsa's ice powers to find a solution.
It could be Orochimaru. Imagine he discovers the power of the ocean in Moana's world and wants to use it for his own dark experiments. He could start corrupting the sea creatures and causing chaos on Moana's island. Naruto, having faced Orochimaru before, would know his weaknesses and team up with Moana to stop him.
Obviously, Naruto and Moana would be the main characters. They are from their respective universes and would be the ones driving the story forward in a crossover. Their different personalities and abilities would create interesting interactions.
One possible plot could be that Moana's island is threatened by dark magic from the Harry Potter universe. Harry, Hermione, and Ron could be transported to Moana's world while on a mission to stop the spread of this dark magic. They would team up with Moana to use her knowledge of the ocean and the island's magic, along with their own wizarding skills, to fight off the dark forces. Maybe they'd have to face off against a wizard who has enchanted some of the sea monsters in Moana's world.
Another concept could be a crossover where some of Naruto's friends like Sasuke or Sakura also end up in Moana's world. They all form a team with Moana and her friends to fight against a dark force that is trying to take over the ocean and the land.
One plot could be that the gods from both pantheons are in trouble. The Greek gods are losing their power due to some dark magic, and the Polynesian gods are being threatened by a new force. Percy and Moana team up to find the source of this evil. Along the way, they face challenges like crossing into different realms and dealing with creatures that are a mix of Greek and Polynesian mythology.
One possible plot could be that Naruto has to go on a special mission with Kurenai. They might be sent to a hidden village where they discover a new type of jutsu that is being misused. Kurenai's genjutsu skills and Naruto's rasengan could be combined in unique ways to fight against the villains using this jutsu.
One possible plot could be that Riddick somehow gets transported to the Naruto universe. He could initially be seen as a threat, but then he teams up with Naruto and the others to fight a common enemy, like a new powerful Akatsuki member who has powers similar to some of the creatures in Riddick's world. Riddick's combat skills and his ability to see in the dark could give the Naruto gang an edge in battles.
One interesting plot could be that Naruto and The Flash team up to stop a villain who can manipulate time. The Flash uses his speed to move between different time periods while Naruto uses his shadow clones to gather information across a large area. They would have to learn to combine their powers and trust each other's instincts in order to succeed.