Hajime Muroto is one of the main antagonists of Gantz. He is a young murderer who kills Hobo's for his own amusement alongside his friend, Ryuji Kajiura.
Hajime was beaten several times by his mother. One day he told his father about this, but his father was enraged and believed it wasn't true, so he beaten Muruto himself. This led to Hajime's insanity as he now lived with another murderer named Ryuji Kajiura and the two murdered hobo's and women. They frequently go out to beat hobo's to death with metal baseball bats for amusement.
One day, some (presumed FBI) agents armed with Pistols found the two at their hideout with a deceased woman and shot them both dead for their crimes and murders. The two then were taken to Gantz to do a mission where they must eliminate the "Kuruno Alien" which Gantz attempted to trick them by saying Kei Kuruno is an alien that must be killed. Hajime held Kuruno at gunpoint to try and keep him on an armed guard while everyone changes into their suits.
On the mission, Hajime and Ryuji planned to kill everyone else and even double cross each other. When Ryuji admitted they killed hobo's, Hajime lied and claimed his forcing him to commit crimes like murder, which angered Ryuji. The two then took the teacher hostage and took her downstairs where they planned to kill her. As they got there, Hajime killed her with a Knife and then threw her to Kuruno.
Later on, they were hiding at a building with an Armory. Hajime tried to kill them with an assault rifle but Giichi stopped him and said that Ryuji is not going to control him anymore. Though Hajime shown his true colors and pulled out a Rocket Launcher to kill one of the survivors. Giichi then cried as he believed lives were lost because of his choices and so he decided to kill them both before anyone else can get killed. Mika went with him to kill Hajime who got a gun and shot at Giichi. The two were knocked down and so Hajime tied them to a Grenade which if Mika would take the pin out, Giichi dies. For further torture, Hajime got a belt and beat Mika with it. To save Mika, Giichi pulled the pin out, sacrificing himself and severely harming Hajime.
Kuruno arrived and kicked Hajime, believing he killed him, he tried to comfort Mika but Hajime was still alive and beat up Kei. Though after a long fight, Kei tied up Hajime, who thought Kei was going to kill him. Though Kuruno got out the Y-Gun and instead transported him somewhere unknown.
A juvenile delinquent whose hobbies consists of beating hobo's to death with a Baseball Bat, messing with people's heads by blaming all his actions on someone else and basically killing victims whenever possible. He blames his behavior on his mom for beating him up several times.