In a skyless cavern village, Simon toils, drilling holes to expand his stifling world, until he makes an extraordinary discovery: a glowing drill-bit that activates a man-sized mecha! Dragged into a plot to drill to the surface by gang leader Kamina, the ceiling crashes down along with a giant monster! Boisterous Kamina and cowardly Simon, with help from sexy Yoko, must defeat the monster, but what awaits on the surface world?