A Japanese salaryman finds his body transforming into a weapon through sheer rage after his son is kidnapped by a gang of violent thugs.

A businessman, Tsuda, runs into a childhood friend, Kojima, on the subway. Kojima is working as a semiprofessional boxer. Tsuda soon begins to suspect that Kojima might be having an affair with his fiancée Hizuru. After an altercation, Tsuda begins training rigorously himself, leading to an extremely bloody, violent confrontation.