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.
The Gantz opens, revealing unusual weaponry and odd suits. The strangers are sent into the city, ordered to kill an alien that roams the streets - and then the carnage begins.
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. But will it help him when Kishimoto appears at his door?
Despite his best efforts, Kei remains unsatisfied during Kishimoto's overnight stay at his apartment. At the place Kato calls home, more ugly evidence of abuse piles up.
Kato's patience is being tested. At home, the abuse dished out by his aunt pushes him to the breaking point. Meanwhile, at school, a group of bullies forces him to take decisive and drastic action.
A new round begins for the gang. Appearing before the Gantz, they find themselves joined by a diverse group of fresh players. As the game gets underway, Kei panics when he realizes his suit is nowhere to be found.
As the group prepares to track down the Suzuki alien, Tetsu's gang is creating conflict and Nishi's smart mouth isn't helping the situation. When tensions boil over, blood is spilled before the hunt even begins.
Without his suit, Kei finds himself in serious jeopardy when he captures the attention of the Suzuki alien. Nishi ends up in even graver danger when his suit malfunctions at the worst possible time.
Kato is forced to take action to save Nishi from certain death, but he may not be ruthless enough to kill the Suzuki alien. Time is running out for yet another player trapped in the cruel world of the Gantz.
The group is beginning to figure out the rules of the twisted game in which they are caught, but survival is still far from guaranteed as the battle with the remaining Suzuki aliens erupts.
Kei, suitless and outnumbered by the Suzuki aliens, must face the biggest monster alone. When the battle ends and the scores are tallied, the group sees that there might be a way to escape their strange fate.
