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Gantz (ガンツ) is a Japanese manga and anime series written and illustrated by Oku Hiroya.
A pair of high school students, Kurono Kei and Katou Masaru, are seemingly run over by a subway train, after saving the life of a homeless drunk who had fallen onto the tracks. Following their untimely deaths, Kei and Masaru find themselves transported—alive and well—along with a number of people who have also just died, to the interior of an unfurnished Tokyo condominium from which the Tokyo Tower may be seen—and none of them are able to leave. At one end of the room is a featureless black sphere known as "Gantz".