In the past, a 14-year-old sadistic necrophiliac named Kosuke Kira was arrested for murdering three women. Back in the present, a lawyer named Soichi Natsume discovers Kosuke near the shore, skewering frogs for fun. Soichi tries to explain that it is wrong to kill living things out of amusement, but Kosuke rejects the explanation. After a food supply drops nearby, the two investigate it with Kosuke's abusive father, Yoshihisa Kira. Yoshihisa, after forcing his son to use an Implosion BIM to retrieve the food supply from a tree, decides to take the case for himself, going on about the survival of the fittest. Kosuke, tired of the abuse, activates an Implosion BIM on Yoshihisa and kills him, feeling a rush of euphoria. Soichi runs away frightened, saying Kosuke is akin to a monster. At this point, Kosuke is discovered by Ryota and Kiyoshi, who retreat after failing to reason with him. As Kosuke chases after them with the intent to kill, Ryota decides to fight in order to protect Kiyoshi. Ryota and Kosuke soon recognize each other as Btooom! players and engage. After Kosuke taunts and attacks him, Ryota hits his head against a rock, which causes a personality shift where he perceives reality as being the game world. Ryota defeats Kosuke by hiding his movements with advanced sonar cancelling. Although Ryota cannot bring himself to kill Kosuke, Ryota binds him to a tree, taking his food supply and BIMs. When Ryota leaves, Kosuke is thrilled to learn Ryota is actually the top ranked Japanese player of Btooom!.