The Lost Ones are strangers from another world, hailing from a place no one has ever heard of called "Japan." These wanderers have been associated with catastrophes since many years ago and the solemn duty of exterminating them without remorse falls to Menou, a young Executioner. But when her mission is complicated by a Japanese girl named Akari who refuses to die, Menou embarks on a peculiar journey to find something that can slay even an immortal who insists on traveling with her wouldbe-killer!

The ritual to kill Akari has begun, and everything is going smoothly. Menou believes this will finally be the end of the Otherworlder—until she receives word from Momo of Orwell's betrayal. The archbishop has woven an intricate plot and will use even taboo conjurings to achieve her goal. In the face of her staggering power, can Menou and the others hope to survive?

In order to kill Akari, Menou follows Orwell’s orders and boards a train to Garm. Unbeknownst to her, terrorists bent on capturing the princess Ashuna sneak onboard. Will Menou be able to deal with these unexpected foes on the runaway train, or has she met her match?