Tetsurou Okino, a young engineer, is transferred to Hato Industries, a vermin extermination company, bringing with him the new robot Bullbuster that he developed himself. At Hato Industries, a small and cash-strapped firm, President Tajima and his team face off against a mysterious creature. The operation is constrained by strict budgets: fuel costs for robots, labor costs for pilots, and the fact that wasting even a single bullet is unacceptable. Caught between their ideals of extermination and the reality of their finances, what does the future hold for Hato?