Ranmaru is a 450-year-old vampire who works in a bathhouse. As a vampire he is particularly picky about his blood choices, his main goal being to drink the blood of an 18-year-old virgin. To do so, he has been watching 15-year-old Rihito, the son of the bathhouse owner who saved him from near death. Rihito must not lose his virginity before he turns 18 and Ranmaru does everything he can to prevent that. However, when Rihito starts to show interest in a classmate, Ranmaru's desperate fight to preserve the boys virginity begins.