Gantz
Gantz, 간츠, 殺戮都市
Gantz (ガンツ Gantsu) is a Japanese manga and anime series written and illustrated by Hiroya Oku. Gantz tells the story of Kei Kurono and his friend Masaru Kato who die in a train accident and become part of a semi-posthumous "game" in which they and several other recently deceased people are forced to hunt down and kill aliens armed with a handful of futuristic items of equipment and weaponry.
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 featureless black sphere known as "Gantz".
(Wikipedia: The Free Encyclopedia, s.v. "Gantz")
