Shoutarou Kaneda finds out that he has an older brother who can also control the Tetsujin 28. Also named Shoutarou, the young man is a surviving soldier of a forgotten squad that has finally returned to his homeland after ten years of isolation not knowing that the war had long ended. Parallel to this discovery, a new kind of bomb is located under Tokyo. Created by the late professor Kaneda, the Ruin Bomb has the power to destroy artificial buildings in a large area while keeping living beings (with the exception of plants) unharmed. It is up to young Shoutarou to find out what is the professor's true legacy.