The movie stars Sonny Chiba as astronomer Shinichi Tachibana, a man who has a secret identity as superhero “Iron Sharp” (changed to “Space Chief” in the English dub) and has many children as friends.
When they are attacked by a group of metallic aliens (“Neptune Men” in English), Iron Sharp drives the aliens away. Tachibana is also resourceful, as he helps develop an electric barrier to block the aliens from coming to the Earth. After several losses by the aliens, they announce that they will invade the Earth, throwing the world into a state of panic.
As they invade the aliens destroy entire cities with their mothership and smaller fighters. Iron Sharp destroys multiple enemy ships and Japan fires a nuclear missile at the mothership, destroying it.