Height: 168 cm Kurono Kei is the protagonist of Gantz. He is a 10th grader summoned by Gantz, along with Kato, after being hit by a subway train in an effort to help a hobo passed out on the tracks. Initially Gantz refers to Kurono as "Bitch" and "Loser", though he settles on "Kurono" as the series progresses.

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Kei constantly shows the ability to improvise and see the bigger picture. He also seems to be a quick thinker in the midst of combat, demonstrating the ability to find his enemies' vulnerable points, quicker than most. He shows excellent use in all of the Gantz equipment, favoring the various guns, while occasionally using the Katana in which he shows great proficiency using. In the beginning, he is a rather selfish character who often ends up being the reluctant hero. Unlike the rest, he has sense to take an x-gun home and test it out. In doing so, he figures out that the x-shotgun can lock onto multiple targets and fire at them all at once. On his third mission, Kurono starts a relationship with a woman named Sei who she just meet with. Unfortunately, the mission is quite the disaster, and she dies, alongside Kato and all of the others members, leaving Kurono as the sole survivor. At one point, Kurono actually enjoys the brutal missions, having a chance to prove his mettle and to use the power Gantz's technology grants him to decimate his foes, as well as to receive the admiration of his team members (such as Sei or Kishimoto). This ceases after the death of Kato, where he becomes frightened of the missions and hesitates to act as recklessly as he had in the past. Another deciding factor in Kurono's decision to prioritize brains over force is his growing attachment to Kojima Tae. He starts to believe that he must come back alive in order to be with her.

After the events of Gantz Second Stage:

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Kurono is forced to go alone in his next mission, as a form of punishment by Gantz for throwing a tantrum and demanding his friends be resurrected. On this mission, his fourth, he manages to kill a large group of winged, child-like looking aliens, but one survives and kills almost all of Kurono's schoolmates as a form of revenge. Kurono, the more experienced member of the team at the time after the Buddhist Temple mission, is eventually regarded as a hero by the other players who look up to him. He becomes the leader of the team and decides to take up the mantle of Kato's philosophy that everyone should come back alive, wich is ironic considering that Kato had tried to model himself after Kurono's younger self. In order to increase the survival of the Gantz Team members, Kurono holds regular meetings at his apartment where the team discusses missions and practice using the suits. These meetings appear to help greatly during the Oni mission as nearly all of the members survive in spite of the outstanding and powerful number of enemies. At the end of the mission, Kurono requests the revival of Kato and Nishi Joichiro. After the first mission of Phase 2,Kei is revived by Kato but remembers nothing beyond his choice to leave the game. Receiving the news from Nishi that the world will end in 1 week, Kei spends more time with his girlfriend Tae and is seen at the Tokyo Gantz team meeting with Nishi talking about the "End of the World" in 1 week's time. As Kurono enjoys and wastes his last days together with Tae, Reika visits his apartment and confesses her love to him, asking to sleep with him. He rejects her saying he can't understand as to why she would have any feelings for him and tells her they are "worlds apart", mentioning that he is just a High school student and she is a celebrity. Kurono and the team are sent to Italy where the final battle with the Roman aliens takes place. He and the rest of his team witnesses the amazing power of the Roman statue aliens as they break his and Kato's Gantz Sword with ease. Even with assistance from other Gantz Teams, some of Kurono's team members perish in combat. At the end of the mission, Kurono yells at Gantz for not resurrecting Suzuki after being requested to by Reika. He later calms down and leaves the room with everyone. Unknown to the others, then Reika comes back into the room, and ends up resurrecting a second Kurono instead of Suzuki, although unwillingly. The Kurono "copy" appears with his suit on and an Z-Gun in hand. After meeting the original Kurono, the copy decides to live with Reika. The original Kurono stays with Tae but both are separated when a new race of aliens invade and occupy the planet; Tae is abducted in the process. As the original Kurono searches for Tae, the copy assembles with other Gantz members from across the world who wish to save humanity from the aliens. During one of these fights, Reika dies while saving the copy, leaving him with a death wish; he dies when confronting the aliens responsible for the invasion and the Gantz network. The original Kurono manages to save Tae and a large group of humans from the invaders. However, the aliens demand to face Kurono, having labeled him as the strongest fighter on Earth. Kei by this point is skilled enough with the Gantz Sword to fight on par with and even injure the notoriously fast Eeva Gund, most likely the Katasrophe Aliens' greatest warrior. This is a considerable feat, given the fact that Eeva doesn't seem to have been injured by anyone except from Kei. Kurono accepts the challenge and thanks to Kato and his other allies, he succeeds in defeating the aliens' champion. Following the final fight, Kurono and Kato are received on Earth as heroes.