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 of whom has suffered a different 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 that secretly live on Earth, or face final death themselves.