To fight a deadly virus, an implant was developed for transplantation into the human nervous system. Unfortunately, this technology was also exploited by unscrupulous parties to create human weapons, blood-red-eyed creatures known as "Roido." To counter this threat, the defense agency established the Karakuri unit, an elite force whose human members are monitored by small talking animals. As Kiru, a karakuri, visits his friends Koten and Koron while on leave, he is about to discover that there are no days off when facing the Roido!