The story takes place on Antengai, a solitary island cut off from the outside world that functions as a single, chaotic town where humans and ayakashi coexist. Ayakashi are formless masses of negative emotions that survive by possessing humans and feeding on their spiritual energy, with those possessed known as ayakashi-tsuki.

The young information broker Jen Sanbern, whose family has the traditional duty of recording all events in the city, leaves behind his twin sisters Niya and Riya to embark on a journey. He seeks to uncover the truth of Antengai, a place shrouded in mystery with its communications to the outside world severed. During his investigation, Jen reaches the Human Wholesaler, a forbidden and dangerous entity that he was never meant to encounter. As punishment or consequence, Jen is transformed into a Mailman, one of the beings of identical appearance seen throughout the streets.

Transformed and stripped of his original form, Jen must face new trials to recover what he has lost, including his precious family and his own identity. The narrative follows his struggle to reclaim his heart, both literal and metaphorical, as the city’s final truths are revealed. The work functions as a conclusion to the series, unraveling the mysteries of the closed island.

Lurking within the setting is the Tanchou Angel, a being believed to be a type of ayakashi that takes those who have led pitiful lives to paradise. Other inhabitants include a blind boy named Lucksain, who is given an artificial eye. The narrative arcs progress from establishing the world through various character vignettes involving a killer smoke pipe, a color insect master, and other eccentric residents, before converging on the central threat of the Human Wholesaler and the fate of the Mailmen, culminating in a final confrontation that decides the future of the dying town.