Hoichiro Ohma leads a double life as an unremarkable office worker and the clandestine Judge of Darkness, a hereditary enforcer of justice beyond human law. By day, he blends into the corporate grind as a reserved, low-ranking employee, unnoticed by colleagues. By night, he invokes ancient edicts from the Laws of Darkness—recorded in a human-skin tome—to prosecute crimes eluding mortal courts, aided by a parrot skilled in mimicry and reconnaissance. His moral code permits lethal retribution for atrocities like murder, embezzlement, or corporate malfeasance.

Central to his missions is dismantling the empire of Koji Kawamata, a corrupt executive entangled in financial fraud and assassination plots via South American mercenaries. To deliver judgment, Ohma collaborates with underworld entities: the Hag of the Styx ferries souls, while the Court of Ten Kings oversees trials in their shadowy realm. A climactic showdown pits him against a metaphysical defense attorney, culminating in Kawamata’s guilt being unmasked by Enma’s Mirror before the Ten Kings.

Nanase, a secretary at his workplace, unknowingly supports his dual endeavors, providing both emotional grounding and accidental aid during supernatural confrontations. Though adversaries occasionally outmaneuver him, his resolve is fortified by a familial duty spanning centuries. The narrative focuses narrowly on his role within corporate corruption cases, omitting deeper backstory. No expanded lore exists beyond the original 1987–1991 manga and its 1991 OVA adaptation.