The Heterodyne aliens, who disappeared abruptly, have resurfaced after thirteen years, catching everyone off guard. To ward off the impending danger, a group of three office workers employed by 21st Century Security Corporation are tasked with operating Dai-Guard, a gargantuan robot once deemed useless. However, the robot has fallen into disrepair over time. Despite this setback, the determined salarymen are unwavering in their efforts to protect the planet.