Gauche Suede commands great respect among the Letter Bees, a state agency responsible for delivering written correspondence to even the most isolated areas. Yet, the Amberground, the territory Gauche must cross, is shrouded in perpetual twilight and inhabited by creatures called Gaichuu. During one perilous trip, Gauche encounters Lag Seeing, a distressed young boy who has been dispatched as a letter. Five years later, Lag becomes a Letter Bee himself, motivated by his travels with Gauche. In his effort to emulate his hero, Lag uncovers the strife and intricacies at the core of his world.