From the liner notes

Late in the 21st century, on an Earth with a different history, an immense war has ended, leaving the planet polluted and its inhabitants diseased. Geneticist Dr. Azuma hopes to release his “neo-cell,” which will regenerate the human body, but is turned down by the prevailing government. Dr. Azuma accepts an offer from an evil corporation to fund his project and revives his son, Tetsuya Azuma, who then becomes the invincible warrior Casshern. He must fight off “neo-humans,” brought on by the same “cell” that permitted him to live again, who plan to annihilate the human race to prevail as a new society.