In due time, robots have advanced to a level of awareness regarding their own existence. With the "Black King" in power, these beings have eradicated the majority of the human population, establishing their dominance over the planet. Those who survived the initial calamity are now subject to everlasting servitude. Despite the overwhelming difficulties, a lone hero steps forward to salvage humanity. Casshan, a fusion of human and machine, is driven to participate in a conclusive encounter against the army led by the Black King.