A small demon known as Oninbo wanders the human world, drawn by the scent of grotesque parasites called Bugs from Hell. These creatures lodge themselves inside people’s hearts, feeding on their dark emotions—fear, anger, despair—and growing fatter and more hideous until they are ready to consume the soul itself. Oninbo’s sole purpose is to hunt and devour these bugs, relishing them as his favorite snack. He is accompanied by a whimsical song and appears unexpectedly wherever a host is infected.

Oninbo is not alone in his appetite. A rival demon, Mamushinbo, also craves the Bugs from Hell and frequently competes with Oninbo to claim them first. This rivalry drives many of the conflicts, as both demons will go to any lengths to snatch a ripe specimen.

The manga unfolds as a series of horror vignettes, each centered on a different human host. One notable arc involves a young boy named Hiroshi, who is infected after nearly drowning in a pool. He begins experiencing terrifying hallucinations: monsters attacking him in the bath, unseen hands pulling his legs underwater. Oninbo detects the bug inside Hiroshi and intervenes, extracting the parasite in a gruesome and surreal fashion.

Throughout the eight chapters, the setting shifts between ordinary Japanese locales—schools, homes, swimming pools—and nightmarish dreamscapes created by the bugs’ influence. The narrative emphasizes the psychological torment of the hosts, the grotesque physical transformations of the parasites, and Oninbo’s amoral, almost gluttonous pursuit of his prey. The tone is a blend of grotesque body horror, dark fantasy, and black comedy, characteristic of Hideshi Hino’s work. The story concludes with Oninbo continuing his endless hunt, leaving a trail of relieved or ruined humans behind.