Kōsuke Kira

Kousuke Kira was a troubled child, having been physically and sexually abused by his father. As is often the case, Kira himself developed criminal tendencies, starting in petty thefts, but culminating the murder and post-mortem rape of several women. Kira was arrested for his crimes, but thanks to a lawyer named Soichi Natsume, he received a light sentence because of his past.

Sometime after Kousuke's presumed incarceration or institutionalization, Kousuke, his father, and Natsume were all chosen to participate in an illegal "death game" run by Tyrannos Japan, makers of the video game BTOOOM!, a multiplayer game where the players are armed only explosives such as grenades and mines.

The "death game" participants were chosen by a random draw of replies to a chain letter that asked the recipient to name someone they wanted to die. Kousuke and the other people chosen were kidnapped, placed in cargo plane and explained that they would be given eight explosives of various types, called BIMs. The participants were then forced into automatically opening parachutes and thrown out of the plane, onto an uninhabited island. The only way off the island was to kill seven other players.

Kira is introduced killing small frogs with a wooden staff just for his own amusement while walking with Soichi Natsume, who, tells him that he should not fear him and stand up to him. The two of them meet up with Kousuke's father, who, after Kousuke angers him, attempts to sexually assault him. Kousuke, taking Natsume's advice in his own twisted manner, activates an a special BIM which creates an implosion through unknown technology and destroys everything within about ten feet. Kousuke affixes it to his father's shirts and escapes as his father tries to remove it, but the grenade activates and implodes while his shirt is over his head, completely destroying much of his upper body.

After killing his father and taking his high explosive BIMs, Kousuke goes on alone, engaging the series protagonist Ryouta Sakamoto in combat, though both survive the encounter, and later killing a second combatant, a member of a team of four, also with an implosion grenade. It is not known what happens to Kousuke after this point.