Gantz

A couple of high school pupils, Masaru Kato and Kei Kurono, are hit with a subway train in a effort to save the life span of a drunk homeless guy who’d fallen onto the tracks. Following their deaths, Kato and Kurono find themselves transported to the inside of an unfurnished Tokyo flat, where they meet with a Gantz expert Joichiro Nishi, as well as other clueless players. The pair soon understands that they’re prohibited to depart the flat. At one end of the room there’s a sizable black sphere called “Gantz”.