- College student Kei Kurono (Kazunari Ninomiya) notices former childhood friend Masaru Kato (Kenichi Matsuyama) helping a drunk man who fell from a subway platform. Kei Kurono then jumps down to help his childhood friend. A few moments later, the subway train rapidly approaches and both men look on helplessly on as their life is about to end.
The next moment, Kei Kurono and Masaru Kato finds themselves in a strange apartment with a mysterious giant black sphere and others who have recently died. The massive black sphere in the center of the living room is "GANTZ". GANTZ then assigns the people gathered in the room on missions to exterminate aliens. They are given a set time and if successful will receive points. A total of 100 points will allow them to leave this purgatory like place or send someone else back to life. If they fail, they can perish forever ...