Several years ago, Doctor Hoarai predicted that a race of subterranean rock people was preparing to attack humanity. Nobody believed him, but the scientist built mecha in preparation for the attack. Following his death, Hoarai's equipment is discovered by five young people who believe in his cause. They use the mecha to defend humanity as a team of heroes. The team is led by Yoko Misaki, the female strategist of the group.
