The novelization of Rosario Vampire is a great read. It stays true to the core elements of the source material while introducing new elements that enhance the narrative. It's a must-read for fans of the series.
One manga that could be similar is 'High School DxD'. It features supernatural elements and a focus on a group of students with special powers and their adventures.
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.
A fanfiction could focus on a love triangle situation involving Mizore, Moka, and another character. Mizore has always had a secret admiration for Moka, but Moka is oblivious to it. Meanwhile, a new character enters the scene and shows an interest in Moka as well. Mizore then has to decide whether to be upfront about her feelings or keep them hidden. This could lead to a series of comical and emotional events as Mizore tries to navigate her emotions and the new situation in the Rosario Vampire world.
One possible fanfiction could be about the OC being a new student at the school. Mizore, being the shy and mysterious yuki - onna, is initially hesitant to interact with the OC. But as the story progresses, they could be paired up for a school project. This would force them to spend time together and gradually discover each other's personalities. Maybe the OC has a special ability that Mizore is curious about, and that becomes the starting point of their relationship.
The ending of Rosario Vampire manga is quite complex. The main characters face some major challenges and their fates are tied up in a way that leaves readers with a sense of closure but also some room for interpretation.
The Rosario Vampire manga ends with a climactic showdown and resolutions for the main characters. It leaves some room for interpretation but offers a satisfying conclusion to the series.