The prestigious Cross Academy, a private boarding school, is attended by two groups of students: the Day Class and the Night Class. At twilight, when the students of the Day Class return to their dorm, they cross paths with the Night Class on their way to school. Yuuki Cross and Kiryuu Zero are the guardians of the school, there to protect the Day Class from the academy's dark secret: the Night Class is full of vampires. — from Viz

Yuuki's earliest memory is of a stormy night in winter, wherein she was attacked by a vampire... and then rescued by another. Now ten years later, Cross Yuuki, the adopted daughter of the headmaster of Cross Academy, has grown up and become a guardian of the vampire race, protecting her saviour, Kaname, from discovery as he leads a group of vampires at the elite boarding school. But also at her side is Kiryuu Zero, a childhood friend whose hatred for the creatures that destroyed everything he held dear, now determined never to trust them.

This coexisting arrangement seems all well and good, but have the vampires truly renounced their murderous ways, or is there a darker truth behind their actions? Is Kaname's infatuation with Yuuki the beginning of a forbidden romance, or is it something in her forgotten past that draws him to her? In this world of secrets, nothing is as it seems, and the price of misplaced trust may even be worse than death.

[Source: AniDB]