The Lost Ones are wanderers from a distant world known as "Japan," and no one knows why or how they left their homes. The only certainty is that they bring disaster and calamity. Menou, a young Executioner, is tasked with exterminating them without remorse. When she meets Akari, it appears to be just another job...until she discovers that killing this girl is impossible! And when Menou starts looking for a way to defeat this immortality, Akari is more than happy to accompany him! So begins a journey that will forever alter Menou...