While on a vacation cruise with his parents Yu Arashida witnessed the death of his parents when a gigantic robot attacked his ship ultimately destroying it along with everyone on board, Yu was the only survivor. Flash forward several years into the future and Yu is now a grown up man being trained by his grandfather to pilot Earth's ultimate defender, Mach Baron, a giant red robot designed by his late father and constructed by his Grandfather.

After his grandfather is assassinated by an evil organization whose goal is to conquer the world Yu becomes Mach Baron's pilot and along with the members of KSS (Kokusai Kagaku Kyojo Tai) will fight to defend the Earth from falling into the hands of these evildoers and their giant robot machines.