The game takes place 8 years after a great war was waged between colonies in outer space, and peace has finally settled back onto the Earth. The main character, a 17-year-old war orphan named Tadashi Himukai, purchases a used worker-mech in order to start a construction business with his girlfriend, Elina Furfa. However, when he first activates it, the worker-mech disguise falls away, revealing a combat model Metal Slader, which were all supposedly dismantled after the war, and an enigmatic message is displayed in the cockpit: "EARTH IN PERIL... SEEK THE CREATOR". Prompted by this warning, Tadashi, his sister Azusa, and Elina head out into space to find the answers behind it.