GANTZ [Street o21]

A pair of high school students, Kei Kurono and Masaru Kato, are hit 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 large 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, with three racks protruding from it, that offer various items for them to use. These include the custom fitting black suits Gantz made for each of them, giving them super-human strength, speed, stamina and relative invincibility, a controller which acts as a radar and stealth unit, and three types of weapons.

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 orders 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. Once a participant has scored 100 points, a "100 point menu" will appear. The menu offers three options. The first option allows the participant to return to their normal life, not to summoned by Gantz again. Their memories of Gantz and the missions will be erased. The second option grants the participant an extremely powerful weapon. The third and final option allows the participant to revive someone who has died during a mission from Gantz' memory. After a mission has been completed, and points have been tallied up, the participants are then allowed to leave, and live their lives as they see fit until Gantz summons them back again for the next mission. During the third mission that Kurono and Kato participate in, almost all of the participants are killed, including Kato, which leaves Kurono as the sole surviving member of the "Gantz team". 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, a boy named Nishi, who knows a lot about how Gantz works, opens the "catastrophe countdown" which the other players were unaware of. Once opened, the countdown shows that there is one week left until "catastrophe", it also frees all the participants from the game. A week later, a massive alien force invades the Earth and begins exterminating the human race, while Kurono and his companions try their best to make use of Gantz' advanced technology and weaponry in defense. The Japanese also learn of the existence of Gantz teams all around the world. After a long battle, the humans armed with Gantz weaponry managed to stop the alien invasion and soon after, Kurono and friends are brought into contact with another alien species who is revealed to be the ones who provided mankind with the means to defend itself against the invaders.