College student Kei Kurono (Kazunari Ninomiya) witnesses his childhood friend Masaru Kato (Kenichi Matsuyama) attempting to help a drunk who has fallen onto the subway train tracks and spontaneously jumps in to help him. However, both are run down by the oncoming train... In the next instant, they are transported to a strange apartment with others who should also be dead. In the center of the living room is an enigmatic black orb known as 'Gantz'. Gantz enlists each of them on a mission to hunt down and exterminate 'aliens', providing them with fighting suits and weapons.