Kei Kurono is a typical high school student in a selfish world, not caring about anyone other than himself. However when, by chance, he was forced to help his childhood friend, Katou Masaru, rescue a drunkard who fell into subway tracks, both he and Katou were killed... Or not. After being run over by the train, they were suddenly teleported to an enclosed apartment with others who recently died. And now their lives are controlled by a mysterious black ball inside the apartment called GANTZ, and they are forced to participate in a "game" of unprecedented danger and horror.

Gantz is based on an 18 volume manga by the same name. The Gantz manga is much more explicit than the anime with regards to violence, language, sex, nudity, and general harshness. However it is also widely regarded as being much better and more detailed.