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, and in the middle of the room is a bizarre black sphere: the Gantz.

The Black Globe interrupts a fight between Katou and the Yakuza, instructing them to kill Neigi Seijin.

With the small alien dead, the large alien exacts his revenge, slaughtering many with the group; when the creature pursues Kei, the young man quickly discovers that his physical abilities are enhanced by the suit he wears.

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.

Seemingly back among the living, Kato must protect his brother from their hateful aunt; meanwhile, Kei's special suit gives him an advantage against the bullies at school.

Two friends are recruited to hunt down aliens.