Lawyer Shindo Kai is an undefeated ace, also working as a hitman who punishes criminals exploiting legal loopholes. While secretly serving justice, he hides his true identity as the illegitimate son of Gondo Heihachiro, a yakuza boss. When Gondo's group is attacked by the rising Mayhem gang, Kai, having recently lost a case due to sabotaged evidence, investigates the betrayal. His pursuit of the truth leads to a bloody reckoning.