Vampire Knight is a manga series by Hino Matsuri, published in LaLa and Shojo Beat Magazines and licensed in the US by VIZ. There is an anime currently in production. Cross Academy 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. Yuki Cross and Zero Kiryu 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. (Description from the official Shojo Beat site).