Hidden in his pocket is a black iron gun. Living in his heart is a jet black soul. The story takes place in Edo in 1853. Roji, a man nicknamed "Zangetsu," is the young head clerk at the shipping wholesaler "Mitsutakaya." A promising young man, Roji has a secret life as a high-ranking executive of the Gihei faction of moneylenders who control the underworld of Edo. As he plots to rise within the organization, Roji's weapon is the most advanced revolver of the time, the Colt M1851 Navy! With his well-honed gun skills and natural courage, Roji tries to rise in Edo's underworld.