An aging ruler attempts to divide his kingdom peacefully among his three sons, but is driven to madness when they turn against him.

Set in the late 21st century, Earth is in crisis and the future of mankind is at risk. Hope lies in a geneticist's discovery of a "Neo-Cell" which can rejuvenate the human body, but it is used by an evil corporation to create a race of mutants bent on the annihilation of humanity. A powerful warrior, Casshern, emerges in the battle against this new menace. Only he can save the human race as it fights an ultimate war against its own extinction.