Gantz

In the year 2000, Kei Kurono and Masaru Kato are two high school students who are killed in a train accident. They awaken in a strange room with a large black sphere called Gantz. Gantz explains that they have been chosen to participate in a game in which they must hunt down and kill aliens that have invaded Earth. If they succeed, they will be rewarded with points that can be used to purchase weapons and equipment. If they fail, they will be killed and their memories of the game will be erased. Kei and Masaru are joined by a group of other players, including the mysterious Kurono Tae, the skilled sniper Reika Shimohira, and the powerful cyborg Keisuke Izumi. Together, they must face an ever-growing number of aliens as they fight to survive in a world where the rules are constantly changing. Gantz is a dark and violent series that explores themes of death, sacrifice, and the nature of humanity. It is a story about the lengths that people will go to survive, and the sacrifices they are willing to make for those they love.