One idea could be a crossover with the Harry Potter universe. Sasuke with his Rinnegan could be a mysterious new student at Hogwarts. Maybe he's on a mission to find a powerful magical artifact that has a connection to his ninja world. Another plot could involve a crossover with the DC universe. He could team up with Batman, both being brooding and powerful in their own ways. Sasuke's Rinnegan abilities would be a great addition to their crime - fighting efforts.
Well, consider a crossover with the Star Wars universe. Sasuke with his Rinnegan could be like a powerful Sith or Jedi - like figure. He might be drawn into the conflict between the light and dark side of the Force. His Rinnegan - related abilities could be seen as a new form of Force power. He could cross paths with characters like Luke Skywalker or Darth Vader and have some epic battles or form unexpected alliances.
One idea could be Sasuke traveling to a different dimension where the Rinnegan has different powers and he has to adapt. Maybe he meets an alternate version of himself with a unique Rinnegan ability.
One plot idea could be that Naruto and Sasuke discover a new power related to the Rinnegan that can only be accessed when they combine their chakra. Another could be a time - travel plot where they go back in time to prevent the creation of the Rinnegan in the wrong hands. Maybe they have to face an enemy who has a corrupted version of the Rinnegan powers and they must use their own understanding of the power to defeat them.
Well, a cool plot for a Rinnegan Naruto crossover fanfiction could be that there is a rift between the Naruto world and a world where the Rinnegan is more common. Naruto gets pulled into this other world and has to adapt to the different power system there. He meets characters who have mastered the Rinnegan and has to learn from them to find his way back home. Along the way, he discovers a connection between the two worlds that was hidden for centuries.
One unique plot idea could be Sasuke traveling to an alternate universe where the Rinnegan has different powers. He might have to team up with versions of his former enemies to face a new, greater threat. For example, working with Orochimaru to stop a rogue group of ninja who are misusing the power of a corrupted Rinnegan.
Well, a plot could revolve around a Rinnegan - induced time - loop situation. A character, perhaps Sasuke, gets caught in a time - loop where he has to keep reliving a certain period in the Naruto story but with different outcomes each time due to the influence of the Rinnegan. He has to figure out how to break the loop and in the process, discovers new secrets about the Rinnegan and its origin. This could also lead to him changing the fate of some characters who died in the original story.
A really cool plot for a naruto and sasuke crossover fanfiction could be that they are summoned to a magical realm. In this realm, their chakra is different and they have to learn new ways to use it. They meet strange creatures and make new allies. The catch is that they are being hunted by a powerful wizard who wants to steal their ninja powers for his own evil plans. So they have to outwit him while also trying to find a way back home. This would allow for a lot of exploration of their characters in a new and unfamiliar setting, and also give room for some great action scenes as they use their ninja skills in a magical world.
One idea could be that they are reincarnated in a modern world. Naruto could be a struggling artist and Sasuke a cold - hearted business tycoon. Their past memories start to resurface, and they have to figure out how to deal with their new identities while still having that underlying connection from their past lives.
One idea could be an OC with the Rinnegan who is from a hidden clan. They use their Rinnegan powers to uncover ancient secrets that could change the ninja world. For example, they might find a lost jutsu that was sealed away long ago.
Naruto would be an interesting character to pair with Sasuke. Their long - standing relationship and the contrast between Naruto's positive energy and Sasuke's more brooding nature could create great drama in a crossover situation. Especially when Sasuke has the Rinnegan, Naruto might have to adjust his way of fighting and interacting with him.
One idea could be that Sasuke somehow ends up in the Bleach universe and teams up with Ichigo. They could face off against a common enemy that has powers related to both the Sharingan and the Zanpakuto. For example, a villain who can manipulate souls like in Bleach but also has the ability to copy techniques like the Sharingan.