Perhaps in the fanfiction, Sasuke's Rinnegan could cross over with a magic system from another anime. So, instead of just ninjutsu, he starts using magic spells that are enhanced by his Rinnegan. This would lead to him having to learn new ways to fight and new strategies, like combining Sharingan - based genjutsu with magic - based illusions.
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.
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.
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.
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 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.
One plot idea could be the reborn character having all of Sasuke's memories from the start. This would allow them to quickly adapt and perhaps change some of the events that Sasuke went through in the original story. For example, they could avoid some of the more tragic moments or make different choices regarding his relationships.
One idea could be a fanfiction where Naruto and Sasuke have to team up again to face a new threat from an ancient evil that has been awakened. They have to put aside their past differences completely and combine their powers in a new way. For example, Naruto could use his Sage Mode along with Sasuke's Rinnegan to perform a super - powerful jutsu.
A plot could revolve around Naruto using his Rinnegan powers to fight against an evil vampire clan that is threatening the Hidden Leaf Village. He might discover that the Rinnegan has some special abilities that are particularly effective against vampires, like being able to see their true forms even when they are hidden or being able to nullify their hypnotic powers.
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.
Another interesting plot is the soul - swap. Imagine Naruto and Sasuke swapping souls. They have to deal with living in each other's bodies and understanding each other's perspectives in a very literal way. It leads to some hilarious and also very heart - warming moments as they learn more about each other.
A unique plot could be a story where the protagonist has both the Rinnegan and Jiongu and is hunted by different ninja clans who want to either steal the powers or destroy the one who has them out of fear. This could lead to a journey of self - discovery as the character tries to understand and master these powers while on the run. Maybe they end up forming an alliance with some unlikely allies to fight against their pursuers.