When Ryunosuke’s pet cat dies in an accident, his inventor father resurrects the cat by placing its brain into an android body fashioned as a young girl. The android, Nukunuku, serves as both a companion and sister to Ryunosuke and as a bodyguard for his father. With extreme strength and feline agility, Nukunuku routinely protects Ryunosuke and his father from Ryunosuke’s mother, who after divorcing his father seeks to kidnap them. Her motives are simple: motherly love for Ryunosuke, but she also wants her former husband, the genius inventor, to work on weapons of mass destruction for her weapons company.