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.
In the beginning, he is a rather selfish character who often ends up being the reluctant hero. 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.
Kurono is eventually regarded as a hero by the other players who look up to him (he takes up Kato's philosophy that everyone should come back alive, ironic considering that Kato had tried to model himself after Kurono's younger self). To increase the survival of the Gantz Team members, Kurono holds 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 number of enemies. At the end of the mission, Kurono requests the revival of Kato and Nishi Joichiro.