In an alternate 1888 Japan following the end of the Continental War, fifteen-year-old Buki Kirā emerges from three years of isolation as something less than human. Raised as a weapon since childhood, he understands tactics, distance, and death—but not emotion.

Now working for the Imperial War Correspondence Office, Buki delivers letters from fallen soldiers to the families they left behind: final words, last confessions, and the unbearable proof that someone will never return. Each delivery exposes him to raw grief he cannot comprehend.

When fellow postal worker Yuki Amane begins teaching him that letters carry pieces of people’s hearts, cracks slowly form in the life he was forced to become. Then a final letter arrives—written by the general who once tried to save him—forcing Buki to confront buried memories, war, and the terrifying possibility of learning how to feel again.