The Lost Ones are wanderers from a faraway land known as "Japan." Nobody knows why or how they left their homes. The only certainty is that they bring tragedy and devastation. Menou, a teenage Executioner, is tasked with exterminating them without remorse. When she meets Akari, it appears to be simply another job...until she realizes that killing this girl is difficult! And when Menou decides to look for a solution to combat this immortality, Akari is more than willing to accompany him! So starts a trip that will permanently alter Menou...