Legend has it that if a human surrenders themselves unconditionally to a vampire, they become an eternally loyal servant incapable of betrayal. Shoou Hataru, an ordinary high schooler consumed by absurd guilt over his obsession with women's chests, willingly sacrificed his blood to save a dying vampire. Unbeknownst to him, a century passed in hibernation—and the world outside fell to ruin. Waking up in a post-apocalyptic wasteland where humans are nearly extinct, Shoou is now his master’s sole blood supply. Caught between lethal vampire-hunting cults and deadly conspiracies, can this mismatched duo survive the targets on their backs?