Another plot could involve a crossover between Naruto's world and a character from the Uchiha clan who has the Rinne Sharingan. They could team up to face a common enemy that is threatening both their worlds. Along the way, they would learn from each other's abilities and cultures. For example, Naruto could teach the Uchiha character about the power of friendship and teamwork, while the Uchiha could show Naruto some advanced Sharingan techniques.
A more complex plot might be a time - travel fanfiction. A character from the future with the Rinne Sharingan travels back in time to Naruto's era. This character has knowledge of future disasters that are caused by a misuse of chakra and the Rinne Sharingan. They try to prevent these disasters by guiding Naruto and his friends. But there are also enemies in the past who want to use the time - traveler's Rinne Sharingan for their own evil purposes.
Another plot could revolve around a character who accidentally acquires the Rinne Sharingan and has to learn to control it while being hunted by various groups. Some might want to use the power for their own evil purposes, while others fear the unknown capabilities. This character could start as a relatively weak ninja but gradually become stronger as they master the Rinne Sharingan, forming alliances with unexpected characters along the way.
One plot idea could be a character from Naruto ending up in the Highschool DxD world and having the Rinne Sharingan. They could use its powers in the battles against the devils and fallen angels in the new world.
One plot idea could be that Naruto discovers an ancient scroll that reveals a way to obtain the Rinne Sharingan. This new power then causes a rift in the ninja world as some fear his newfound strength while others see it as a way to finally achieve peace. He has to struggle with mastering this power while also dealing with the political implications.
In some fanfictions, a character from another dimension enters the Naruto world with the Rinne Sharingan. This new character's power throws the balance of the Naruto world off. The story could revolve around Naruto and his friends trying to understand this new power and either make an ally of the character or defeat them to restore peace in their world.
One interesting concept could be the exploration of new jutsu combinations using the Rinne Sharingan. For example, creating unique space - time ninjutsu that surpasses what we've seen in the original series. Another might be delving into the backstory of how the Rinne Sharingan came to be in a particular fanfiction's universe, perhaps it was the result of a long - forgotten experiment.
A possible fanfiction could be about the origin of the Rinne Sharingan having some connection to the world of RWBY. Maybe there was an ancient civilization in RWBY's past that had a similar power, and through some sort of dimensional rift, it influenced the development of the Rinne Sharingan in Naruto's world. This would involve a lot of world - building and exploration of both universes' histories.
One possible plotline could be the main character with the Rinne Sharingan finding themselves in a world where they are surrounded by multiple characters from Naruto in a harem - like situation. They might have to navigate complex relationships while also dealing with the power of the Rinne Sharingan and the threats that come with it.
One interesting plot idea could be a character from the Naruto world obtaining the Mangekyo Sharingan through some strange and unforeseen event. For example, Naruto himself could be exposed to a powerful Uchiha - related jutsu that accidentally gives him the Mangekyo Sharingan. This would completely change his power dynamic and how he approaches battles. He could then have to learn how to control this new power while still maintaining his own ninja way.
Madara Uchiha could be an interesting main antagonist in this crossover. Since he already has strong ties to the Sharingan and was a powerful force in the Naruto series. If he somehow got his hands on the Rinne Sharingan's full power, he would be even more formidable. He could use it to manipulate reality or time, making it extremely difficult for Naruto and his friends to stop him.
One interesting crossover could be a story where a character from Naruto with the Rinne Sharingan somehow ends up in the One Piece world. Maybe they team up with Luffy and his crew to fight a common enemy. For example, they could use the power of the Rinne Sharingan to unlock some hidden secrets in the One Piece world that are related to ancient powers.