A young engineer named Okino Tetsurou who has developed the new robot Bullbuster is transferred to Hato Industries, a company that exterminates harmful animals. There, the company and its president Tajima Kouji are up against a mysterious lifeform named "Kyoujuu." As a small business that is always finding itself short on money, Hato must always account for every expense such as fuel and pilot labor. And of course, missed shots are not tolerated. The company is always stuck between their ideals of Kyoujuu extermination and the reality of the economy.