In the present day, vampires have established a coexistence with humans through a contractual agreement with the once anti-vampire group, "Abraham." As per the contract, vampires are designated as human pets, leading to a widespread trend of owning pet vampires which can be distinguished from their wild counterparts through their collars. Note that wild vampires are still a significant threat.
A teenage boy, Daichi, aspires to have a pet vampire of his own, but his older sister opposes the idea. One night, a wild vampire named Iko intrudes into their home as the siblings discover that their sister's blood is rare and could make her powerful enough to take down the degrading "Abraham" organization. However, the blood does not have the expected effect on Iko, causing her to unwillingly become the pet of Daichi and his older sister.