There could be a fanfiction where the power system of the Rinnegan in Naruto is integrated into the Rosario Vampire universe. For example, the Rinnegan's ability to control gravity could be used in unique ways in the Rosario Vampire world, like controlling the flight of vampires or other supernatural beings. You can start your search on platforms like Fanfiction.net or Archive of Our Own by using relevant tags.
There's a fanfic where Naruto with the Rinnegan gets transported to the Rosario Vampire universe. The story focuses on how he befriends some of the main characters like Tsukune and Moka. His Rinnegan powers are often used in creative ways, like using the Preta Path to absorb the unique energy of the vampires and other creatures in that world.
One idea could be a crossover where Naruto characters end up in the Rosario + Vampire world. For example, Naruto could be mistaken for a powerful yokai due to his chakra. Sakura might study the unique magic in the Rosario + Vampire world. Another could be a vampire in the Naruto world, using their powers in a different way than the normal jutsu.
One interesting fanfiction could be where Naruto, with his Kyuubi powers, somehow gets involved in the world of Rosario Vampire. Maybe he's on a mission and stumbles upon the school. It could be a story full of action and unique character interactions.
One great Naruto - Werewolf - Rosario Vampire fanfiction is 'The Crossover Chronicles'. It has an interesting plot where Naruto finds himself in a world filled with werewolves and Rosario Vampire characters. The story does a great job of blending the different universes together.
One idea could be that Naruto, with the power of the Kyuubi, somehow ends up in the Rosario Vampire world. He could use his ninja skills and the Kyuubi's chakra to face the various supernatural threats in that world. Maybe he teams up with Tsukune and the other characters to protect the school from an even greater evil.
A fanfiction could revolve around a character who is part Naruto character, part Rosario + Vampire vampire, and has the ability to transform into a kitsune. This hybrid character might struggle with their identity, being accepted in both worlds. They could use their Naruto - like ninja skills, combined with vampire strength and kitsune's cunning to go on adventures, perhaps trying to find a way to bring peace between the different universes or factions within those universes.
One idea could be a crossover where a character from Naruto ends up in the Rosario + Vampire world and meets Kuyo. Maybe Naruto himself gets sent there due to a strange jutsu gone wrong. He could be confused by the different rules and powers in that world, and Kuyo might initially see him as a threat or an interesting new addition.
One idea could be a crossover where a character with the Sharingan from Naruto somehow ends up in the world of Rosario Vampire. They could use their Sharingan abilities to detect and combat the various supernatural threats in the Rosario Vampire world, like the vampires and werewolves. Maybe they'd form an alliance with Tsukune or Moka.
Well, for a Sharingan Naruto Rosario Vampire fanfiction, a possible plot could be that Naruto is transported to the Rosario Vampire universe and his Sharingan gives him an edge in understanding the complex vampire and monster society there. He could form alliances with some of the characters like Tsukune. The beauty of fanfiction is that it can take many different directions, so different authors might explore different aspects of how Naruto's abilities and character traits interact with the Rosario Vampire setting.
One great 'Naruto Rosario Vampire crossover fanfic' is 'Naruto: The Vampire Shinobi'. It combines the unique ninja world of Naruto with the supernatural elements of Rosario Vampire in an exciting way. The story follows Naruto as he discovers a hidden part of his heritage related to vampires, and he has to navigate both his ninja duties and this new vampire side.