Ten years ago, Rihito Tatsuno, a young and innocent boy, saved 450-year-old vampire Ranmaru Mori from the brink of death. Since then, Ranmaru has been working at the Tatsuno family's bathhouse, harboring a secret desire: to taste Rihito's virgin blood as soon as he turns 18. However, his plan is jeopardized when Rihito falls in love with a girl on his first day of high school. Jealous and afraid that Rihito's purity will be lost, Ranmaru begins to lurk in the shadows to protect him from any harm. During this operation, the vampire must keep his true identity hidden and ensure that his target's virginity remains intact.