The protagonist, Nihachi Hatoya, was once a promising judo athlete expected to represent Japan in the world championships. However, his dreams were shattered by a devastating injury, leading to his reassignment within the Japan Ground Self-Defense Force. Now placed in the Special Affairs Division, War History Section, Hatoya assists his eccentric superior, Section Chief Takatori, whose work involves investigating and returning undeliverable letters sent from battlefields—letters whose intended recipients remain unknown. The story begins when Hatoya, during his mundane duties, suddenly finds himself standing in the midst of an actual battlefield. With military law experts providing consulting support, this grounded, mystery-tinged military drama explores the weight of history, the pain of forgotten soldiers, and the strange connection between the past and present carried through unsent letters.