In Karakuri by Masashi Kishimoto, predating Naruto, a dangerous virus prompts the creation of an implant inserted into the nervous system. Sadly, this technology falls into malicious hands, leading to the birth of 'Roido' – red-eyed human weapons. To combat this menace, the defense agency forms the Karakuri unit, where human agents are watched over by chatty animals. When Kiru from the Karakuri unit visits friends Koten and Koron during a break, he discovers that the battle against Roido never rests.