Teruaki "9th Man" Kubota
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He also did not care about the other players as he said he wouldn't hesitate to kill Clover if she didn't cooperate while holding a gun to her head.
He became the first victim of the Nonary Game very early on. By entering Door 5 alone which he achieved by betraying the other players, he violated Zero's rules, hence activating the small bomb lying in his intestine and resulting in his gruesome death.
(Source: Zero Escape Wiki)