Menou, an executioner sworn to eliminate the Lost Ones, Japanese people mysteriously summoned into this world who awaken catastrophic powers, takes on Akari Tokitou as what looks like a routine job. Akari turns out to be impossible to kill: every fatal blow resets moments later, undone by a power to rewind time itself. Unable to simply finish the assignment, Menou takes Akari on the road, searching for a way to end a threat that refuses to die.