Kei and his friend Masaru rush to help a homeless man who has fallen onto the subway tracks, only to be struck and killed by a train themselves. However, instead of awakening in the afterlife, the two find themselves in an empty room with a mysterious black sphere in the center: Gantz. "Your lives are over. I decide how you will lead your new life." Kei and Masaru are trapped after their death, but they are not alone. Surrounded by strangers, each with their own tragic fate, they learn the reason for their unexpected survival. Gantz has summoned them to force them to participate in a deadly game. Equipped with special suits and weapons, they must eliminate aliens secretly living on Earth, or face final death themselves.