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 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.
Goku from Dragon Ball Z could be an interesting crossover character. His raw power combined with Sasuke's strategic use of the Rinnegan could make for some amazing battles and interactions. They could learn from each other's fighting styles.
If it's a crossover with the Fairy Tail guild, Natsu would be an interesting character to pair with Sasuke. Natsu is hot - headed and Sasuke is brooding. Their personalities contrast but they are both extremely powerful. Sasuke's Rinnegan powers could be used in combination with Natsu's fire - based magic in battles against powerful enemies. And they could have some great banter as they try to understand each other's worlds.
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.
One great Sasuke Uchiha RWBY crossover fanfiction is 'Sasuke in Remnant'. It really nails the concept of Sasuke being in the RWBY world. The author does a good job of integrating Sasuke's abilities and personality into the RWBY universe. His Sharingan makes for some really interesting interactions with the Grimm, and his brooding nature fits well with the darker aspects of Remnant.
One creative plot is when Sasuke is in a crossover with the Final Fantasy universe. He becomes a part of a party of adventurers. His skills are translated into the game - like mechanics of the Final Fantasy world. For example, his Sharingan could be like a special ability that can analyze enemy weaknesses. Another is when he crosses over to the Star Wars universe. Sasuke could be a Jedi - like figure, using the Force in a way that is influenced by his ninja training. His lightsaber (if he has one) would be a unique weapon, perhaps with some ninja - style modifications.
One possible plot could be Sasuke arriving in the Fairy Tail world. He might initially be seen as an enemy due to his cold demeanor and powerful abilities. But as the story progresses, he could team up with the Fairy Tail guild members. For example, he could form a bond with Natsu. They might start off not liking each other, but when facing a common powerful enemy, they realize they need to work together. Sasuke could teach some of his ninja techniques to the Fairy Tail wizards, and in turn, he could learn about magic from them.
Sasuke would be a very powerful addition to the RWBY world's power structure. His Sharingan gives him enhanced perception, which would be extremely useful against the Grimm. He could easily analyze their attack patterns and weaknesses. Also, his ninjutsu skills like the Chidori and Fire Style: Great Fireball Jutsu are very powerful. In terms of the Huntsmen and Huntresses ranking, he would probably be considered an S - class level threat or fighter due to his abilities.