In a world where humans and supernatural beings have begun to coexist, the Special Operations Squad deals with ongoing incidents between the two races. One night, Rin, a sword-wielding squad member, rushes to a crime scene only to find a blood-soaked vampire princess, Lavia, standing beside a headless corpse of a fellow squad member. Though evidence at the scene suggests Lavia couldn't have done it, she remains the sole suspect as a high-ranking vampire. To convince her commander who insists on detaining Lavia, Rin forms a contract with her: "A pledge to drink no human blood except hers!" With nowhere else to go, Lavia is invited to Rin's home, beginning their cohabitation in search of the true culprit. As they unravel the mystery behind the incident, their daily life of shared blood and emotions gradually deepens into a bond that transcends species...

(Source: Kadokawa, translated)