A young engineer, Tetsurou Okino, is transferred to a vermin extermination company called Hato Industries with the new robot Bullbuster that he developed himself. There, Hato Industries, a small company with little money, and its president Tajima are against a mysterious creature. There are fuel costs for robots, labor costs for pilots, and of course, wasting even a single bullet is unacceptable. Between their ideals of extermination and the reality of budgets, what does the future hold for Hato?(Source: Translated, edited from official website)