Part of a collection (fourth story) of a larger volume of itself, Vampire☆Vampire.

[From ShoujoMagic]:

15-year-old Hina is about to share her first kiss with her boyfriend Natsuki and all of a sudden he transforms into... a vampire named Hibiki!?

16 year-old Luna is a first-year student at Angelica High School. It looks like it's a Catholic High School, as it is run by nuns. Luna's a cute girl, but she gets in trouble a lot for her behavior. For example, during church services, she was in the back asleep and drooling instead of paying attention. It is after one such event of bad behavior that Luna is punished by having to clean the church. She does so, and pauses to examine a beautiful piece of art on one of the walls. It's like a stone carving where a man's body is coming halfway out... (Source: M-U)

Michiru is Akira Tennouzu's number one fan until her mother remarries and he turns out to be her stepbrother...

Ai was your normal, everyday grade teenage girl until one day, she was involved in a fatal car accident. In the hands of the Specialized Secret Police Organization, she was able to be revived. With her newly gained powers acquired through the operation, she becomes a defender of justice. With the mysterious (and a little perverted) bishounen Sagiriya Shinogu as her partner, she fights the forces of evil!
(Source - B-U)