Pursued by the authorities, a ronin assassin named Shino Ashita is taken in by the immoral Bohachi clan, who use the warrior's superior sword-fighting skills to help them seize control of the local prostitution industry. When no longer of any use, the evil Bohachi leader tries to dispose of Shino by getting him addicted to opium and caging him up with a syphilitic whore; but even stoned out of his mind, the assassin proves to be a formidable opponent. With his sword (named Onibouchou - translated as Ogre's Kitchen Knife), Shino hacks into their ranks and leaves rivers of blood wherever he goes.