A kid volunteers to stop being human so his father can turn him into a weapon against the machines his father created. That choice never leaves the show, even when it's blowing things up. Casshan moves through 35 episodes of robot war with the weight of that one decision pressing down on every fight, every upgrade, every moment he realizes what he's lost to stay alive. The action is brutal and inventive for 1973, but what catches you is watching a son become the instrument of his father's guilt.

Dr. Azuma built many robots to help humankind, but a lightning strike during a thunderstorm corrupts the programming of one of them, BK-1. The robot renames itself Braiking Boss, gathers other machines into a vast army and sets out to enslave the human race. Tetsuya, the doctor's son, asks his father to rebuild him as an indestructible android so he can destroy the threat his father accidentally unleashed, knowing he can never return to being human. Soon after, Braiking Boss captures Dr. Azuma and his wife. Now called Casshern, Tetsuya fights to turn the tide of the war and free his parents, joined by his girlfriend Luna and his robot dog Friender. The result is a sci-fi mecha action series built around a hero's war against a robot army.