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.
There is a fair amount of 'gaara x rosario vampire crossover fanfiction'. These crossovers can be really interesting as they combine the unique powers and personalities from both Naruto (where Gaara is from) and Rosario Vampire. For example, Gaara's sand abilities interacting with the vampire and monster - filled world of Rosario Vampire can lead to some very creative and exciting storylines. Some fanfictions might also explore how Gaara would fit into the school - like setting of Rosario Vampire, or how the Rosario Vampire characters would react to his rather stoic and powerful nature.
One common theme is the clash of different cultures. Gaara comes from a ninja world in Naruto, which is very different from the supernatural world of Rosario Vampire. Another theme could be power struggles. Gaara is extremely powerful with his sand powers, and in the Rosario Vampire world, there are powerful vampires and other monsters. There's also often the theme of acceptance, as Gaara has to find his place in this new and strange world, and the Rosario Vampire characters have to accept this outsider.
In a Naruko x Rosario Vampire crossover fanfiction, the plot could center around a tournament. The idea could be that both the ninja world and the Rosario Vampire world participate in a grand tournament to prove which world has the stronger fighters. Naruko would be one of the representatives from her world. She would face off against the various characters from Rosario Vampire. This would lead to some interesting battles and also some unexpected friendships as they learn about each other's cultures and fighting styles.
A possible plot could be that a powerful artifact in the Rosario Vampire world is being targeted by both Hollows and some rogue vampires. Ichigo and Tsukune find themselves on a quest to protect it. Along the way, they encounter various challenges and meet different characters from both universes. The cultural shock between Ichigo's world of Soul Reapers and Tsukune's world of monsters and humans could also add some comedic and interesting elements to the story.
In terms of character interactions, Naruko would bring her energetic and determined personality to the Rosario Vampire world. She would be eager to learn about their magic and powers. The vampires, on the other hand, would be fascinated by Naruko's ninja abilities. Inner Moka could challenge Naruko to a friendly sparring match to test their strengths. Tsukune would try to mediate between them if things got too intense. And the other characters from both worlds would gradually start to understand and respect each other as they interact more. For instance, Naruto's loyalty to his friends could inspire Tsukune to be more assertive in protecting his friends in the Rosario Vampire world, and the Rosario Vampire characters' acceptance of their differences could teach Naruko's friends a lesson about tolerance.
Tsukune and a powerful mage from the other fandom could be an interesting pair. Tsukune's vampiric powers combined with the mage's magic could create some really cool combat scenes and an interesting dynamic as they learn from each other.
One idea could be that the main characters from Rosario x Vampire end up in an alternate universe where they have to face new challenges based on the rules of the other fandom. For example, they might encounter different types of supernatural beings with unique powers.
Begin with a prologue that sets up the situation. Maybe there are strange energy readings in both the Bleach world and the Rosario Vampire world that are somehow linked. Ichigo is sent to investigate in his world, and as he gets closer to the source, he is transported to the Rosario Vampire world. Once there, he is greeted by the chaos of the Yokai Academy. You can then start to introduce the different characters and their reactions to Ichigo's sudden appearance. This will slowly build the foundation for the rest of the story.
Another idea is a crossover where the shinobi powers in Naruto's world are somehow combined with the unique abilities in the Rosario Vampire world. For instance, the vampires' super strength and speed could be enhanced with chakra control. This could lead to a new kind of battle system where characters from both universes have to learn to adapt and fight together against a common enemy, like a powerful dark force that threatens both their worlds.