Vampire Knight

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, protecting the Day Class from the academy’s dark secret—the Night Class is full of vampires!
(Source: Viz Media)
Note: The chapter count includes 15 extra chapters.