After Kei and his childhood friend, Kato, are torn into bloody pieces by a speeding train, they awake in an unfamiliar room, surrounded by strangers. In the middle of the room is a bizarre black sphere: the Gantz.

If you are chosen by the bizarre black sphere known as the Gantz, you are already dead—yet you might be able to reclaim your mortality. First, the Gantz demands that you undertake brutal missions of madness, killing aliens hidden among the population. It is your only chance and you have no choice. You must play this disturbing game. And if you die again—and you likely will—it’s permanent.

The scores are tallied and Nishi explains some of what he knows about the rules of the strange world of the Gantz. The unusual situation grows even odder the next day when Kei wakes—and finds that this nightmare is no dream.