In fanfiction, Naruto with the Kyuubi could be a key figure in a prophecy in the Rosario Vampire world. His arrival could signal the coming of a great war or a new era of peace. He would have to train with the Rosario Vampire characters to better control his power and also teach them some of his ninja techniques. This would lead to a lot of character development and interesting plot twists as they all learn from each other and face different challenges together.
Naruto could be a new student at the Yokai Academy. His presence with the Kyuubi's power would disrupt the balance. For example, the vampires might see him as a threat or a potential ally. He could use his shadow clones to spy on different factions, like the witches or werewolves, to understand the politics of the school better.
Well, perhaps the Kyuubi's chakra has some unique effect on the vampires. It could either suppress their bloodlust or enhance their powers in an unexpected way. Naruto might have to deal with vampires who want to use him for their own gain, while also trying to keep his identity as the Kyuubi's host a secret. He could form an unlikely friendship with some of the Rosario Vampire characters, like Kurumu, who is initially attracted to his power.
Well, he could fit in as a unique addition to the cast. His ninja abilities would be quite different from the normal powers in the Rosario Vampire world. He might be seen as a wildcard, with his speed and combat skills being a big advantage.
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.
In fanfiction, Naruto characters would have to adapt to the different power systems. In the Rosario + Vampire world, there is magic and different vampire abilities. A character like Rock Lee would have to learn to use his taijutsu in a world where there are flying creatures and magic spells. Meanwhile, the Rosario + Vampire characters might be intrigued by the Naruto characters' use of chakra. They could try to learn it, which would create a whole new set of stories and interactions.
His relationship with the Kyuubi could also change in the context of the Rosario Vampire fanfiction. Maybe the Kyuubi senses the unique supernatural elements in this new world and warns Naruto about certain hidden dangers. This could lead to a deeper bond between Naruto and the Kyuubi as they navigate this strange new place together. And Naruto could gain new abilities or ways of using his chakra influenced by the Kyuubi in this different setting.
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.
Naruto would probably be very curious about the vampires and other creatures in Rosario Vampire. He'd be his usual friendly self, trying to make friends. The vampires might be initially wary of him, especially with the Kyuubi's power, but his positive attitude could win them over. Tsukune, from Rosario Vampire, could learn a lot from Naruto about determination and fighting spirit.
In a Naruto, Kyuubi and Rosario Vampire fanfiction, there could be a plot where a character from Rosario Vampire travels to the Naruto world and discovers the legend of the Kyuubi. This character could then try to bring the power of the Kyuubi back to their own world, creating a whole new set of adventures and challenges as they deal with the different cultures and powers in both worlds.
In some fanfictions, the blend starts with Naruto being transported to the Rosario Vampire world. His Kyuubi powers are something completely new there. The power dynamics in the Rosario Vampire world are mainly based on vampire and monster abilities, and Naruto's chakra and Kyuubi - enhanced skills disrupt that in an interesting way.
The Sharingan could be used to see through illusions created by the vampires in Rosario Vampire. Since vampires often have powers related to charm and mind - control, the Sharingan's ability to break illusions would be very useful. For example, if a vampire was trying to hypnotize a character from Naruto, the Sharingan could counter it.
I'm not sure if there is such a specific fanfiction where a character from Rosario Vampire is reading Naruto fanfiction. Fanfiction can be very diverse, but this seems like a rather unique and specific concept. It's possible that it might exist in the vast realm of fan - created stories, but it would be quite difficult to find without a more targeted search.