Tetsurou Okino, a young engineer, is transferred to Hato Industries, a vermin extermination company, bringing with him the new robot Bullbuster, which he developed himself. At this small, cash-strapped firm, President Tajima and the staff face off against a mysterious creature. Operating costs are tight: fuel for the robots, wages for the pilots, and wasting even a single bullet is unacceptable. Caught between their extermination ideals and budget realities, what lies ahead for Hato?