In the near future, robot technology has progressed to the stage of self-awareness. Led by the "Black King," machines have wiped out most of the human population and taken over the world. Survivors of the initial catastrophe have been enslaved for life. Yet, amidst these struggles, a solitary hero emerges as humanity's savior. He is Casshan—a hybrid of man and machine, compelled to fight the Black King and his army to the bitter end.