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.