Naruto, as a vampire, could bring a new perspective to the power dynamics in the Rosario Vampire universe. He's used to fighting for his beliefs and protecting his friends in his own world, and that attitude could influence the characters in the fanfiction. For instance, he might inspire some of the more timid characters to be bolder in the face of danger.
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.
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.
Shirou's projection magic could be really interesting in the Rosario Vampire world. He could project weapons that are effective against the various supernatural beings there. For example, if there are werewolves, he could project a silver - edged sword.
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.
Vampire Anna could be an outcast in the Frozen fanfiction universe. Since she's a vampire, she might be feared by the people of Arendelle who don't understand her new nature. But she could also use her abilities to help protect the kingdom in secret. For instance, she could use her enhanced senses to detect approaching threats.
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.
Tsukune could fit in as an outsider with unique abilities. His vampire powers would be a contrast to the ice - based powers in the Sub Zero world. He might be initially seen as a threat or a curiosity.
Rosario Vampire might be intrigued. It could be fascinated by the unique characters and abilities in Naruto's world.
Daenerys might be seen as a threat by the vampires at first. But then, some vampires could try to form alliances with her. She has a strong will and leadership skills, so she could potentially rule over both humans and vampires in a new order in the 'Vampire Diaries' world. In fanfiction, her backstory as a Targaryen could also be intertwined with the history of the vampires in some creative ways.
The characters would have very interesting interactions. Naruto would probably be curious about the vampires and their powers. The vampires, on the other hand, might be wary of Naruto at first. And if there's a dragon character, it could be a source of awe for everyone. For instance, Naruto might try to befriend some of the Rosario Vampire characters, while they might be hesitant because of his different nature.
Maybe Naruto forms an alliance with some of the main characters in Rosario Vampire. He could use his ninja skills combined with his vampire abilities to fight against common enemies. Like, if there's a powerful dark force threatening both the vampire and human worlds, Naruto could be a key player in the defense.