Kōsuke Kira is one of the Btooom! players. He is believed to be a 3 star player in the world of Btoom!. He is Yoshihisa Kira's son, convicted of murdering 3 women and raping them at the age of 14. In the real life Btooom! game, he has a very sadistic nature and has no qualms about murdering others due of being abused by his father. He is once defeated by Ryōta and loses his BIM's to him but is left alive because of mercy. He wondering the island and manipulating others to trust him. After managing to retrieve two of his BIM's from Ryōta, he kills Shigemasa Kusunoki and gets his set of seeker BIMs. Leading Heitaro Togo and two others to invite him and form an alliance that plans to escape together by eliminating all other players and claiming their chips. However, when trying to corner Nobutaka and Kinoshita, he is once again defeated by Ryōta.