A fanfiction could explore Tsukune's relationship with his vampire side in more depth. Maybe he has to face a situation where he has to fully embrace his vampire nature to save his friends. This internal struggle and how he overcomes it could be the focus of the story.
One idea could be Tsukune learning a new and powerful vampire ability. For example, he discovers he can manipulate shadows in a way unique to him, which helps him in battles against other supernatural foes in the Rosario Vampire world.
Tsukune might have a character arc where he tries to bridge the gap between the human and vampire worlds more actively. He could start a club in the school that promotes understanding between the two species. This would lead to various interactions and adventures with different characters from both sides.
Fanfiction could also center around Mizore and Tsukune training together. Since they both have different powers, they could learn from each other. Tsukune could teach Mizore about human resilience and determination, while Mizore could show Tsukune how to better control his powers, especially when it comes to the more vampiric aspects. Their training sessions could be filled with both comical and intense moments.
Another fanfiction could be about Nekonome getting into trouble and Tsukune coming to her rescue. For example, Nekonome could accidentally break a precious magical item in the school and Tsukune uses his newfound powers to fix it before anyone notices. This would show their loyalty and friendship towards each other.
First, know the characters well. Tsukune is a complex character with his own growth arc. Make sure to stay true to his personality. Also, understand the world of Rosario Vampire, like the different monster species and their cultures. Then, come up with an interesting plot. It could be a new adventure for Tsukune or a different take on his relationships.
Tsukune's vampire form in fanfiction can vary greatly. Some authors might focus on the emotional aspect of him dealing with this new side of himself. He could struggle with the urge to feed on blood, or he might embrace it as a part of his new identity. Additionally, his relationships with other characters, especially Moka, can be significantly affected by his vampire form.
A possible fanfiction could focus on a love triangle between Kurumu, Tsukune and another character. Kurumu is deeply in love with Tsukune, but Tsukune is conflicted as he has feelings for Kurumu but also has responsibilities towards others. This would lead to a lot of emotional drama and interesting character interactions.
One great Tsukune and Kurumu fanfiction could be a story where they go on a magical adventure together outside of the school. They might face some new and powerful enemies that test their relationship and skills.
One possible fanfiction could be about Mizore and Tsukune going on an adventure together in the world of Rosario Vampire. Maybe they have to face a new kind of supernatural threat that has emerged in the school. They could use their unique abilities, Mizore's ice powers and Tsukune's growing vampire - human hybrid powers, to combat this threat and protect their friends.
One possible fanfiction could be about Nekonome and Tsukune going on a secret adventure in the school grounds. Maybe they discover a hidden passage that leads to a place full of magical artifacts. Nekonome's feline instincts could help them navigate through the dangerous parts while Tsukune's growing powers could be used to protect them from any threats.
One possible fanfiction could be about Akasha seeing Tsukune's unique nature among humans and vampires. Maybe she decides to test him in various ways, putting him in situations that make him question his own beliefs and values. Tsukune, in turn, could be both intrigued and a bit frightened by Akasha.
Yes, there are likely some fanfictions out there with this concept. Fanfiction communities are vast and creative, so it's not uncommon to find crossovers like this. You can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own.