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?