The Gantz anime, directed by Ichiro Itano and animated by Gonzo, ran for 13 episodes and had a direct sequel called Gantz: Second Stage, which continued the series for another 13 episodes. Both seasons make up the 26 episode series. It was licensed in North America by ADV Films. The anime series is distributed in the United Kingdom by MVM Films, and in Australia and New Zealand by Madman Entertainment. Dark Horse Comics started releasing the manga in English in June 2008.
A pair of high school students, Kei Kurono and Masaru Kato, are run over by a subway train in an attempt to save the life of a homeless drunk who had fallen onto the tracks. Following their deaths, Kurono and Kato find themselves transported to the interior of an unfurnished Tokyo apartment. The pair soon realize others are present and find that they are not able to leave the apartment. At one end of the room there is a featureless black sphere known as "Gantz".
After some time in the room, the Gantz sphere opens up, revealing a bald naked man with a breathing mask and wires attached to his head, and three racks protruding from it, that offer various items for them to use. These include the custom fitting black suits Gantz makes for each of them, giving them supernatural abilities, a controller which act as a radar and stealth unit, and three types of guns.
When the Gantz sphere opens, green text appears on its surface, informing those present that their "lives have ended and now belong" to him. A picture and brief information is shown of some of the Gantz Targets, Gantz ordering them to go and kill them. All but one target shown thus far, have been aliens living on Earth, which take on a wide variety of forms. After a period of time which varies between missions, everyone except Gantz are transported to the location of the mission.
Those sent cannot return from the mission until all enemies have been killed, or the time limit has run out. If they survive a successful mission, each individual is awarded points for the aliens they have killed. They are then allowed to leave, and live their lives as they see fit until Gantz summons them back again for the next mission. The only way to stop having to participate in the missions is to earn one hundred points, and choose the option to be freed. Several participants, including Kato, are killed through the third mission they are given, leaving Kurono as the only survivor and the new leader from the "Gantz Team". However, as the series continues, Kurono participates with the objective to revive his deceased friends with the 100 points he can obtain throughout the missions. After several missions, Gantz's sphere indicates that the human race will be over in a week for an unknown reason, but it also frees all the participants from the game.