The rules are easy: they have one hour to complete the assignment.
If they are hurt but alive at the end of the time, they are fully healed, but if they are killed, they'll remain dead.
The 25-episodes series aired on MBS between October 6, 2011 and March 29, 2012.
Sentai Filmworks licensed the series in North America, simulcasting it on Anime Network as it aired and releasing the series on DVD and Blu-ray in two collective volumes on September 18, 2012 and January 15, 2013 respectively.
The main opening themes for the series are "sky's the limit" by Shihoko Hirata for episodes 1-8, 10-12, and "key plus words" sung by Hirata featuring Yumi Kawamura for episodes 13-14, 16-22.
As it later rains during the night, Yu feels a strange ambiance as it tries to pull him into the television, but he manages to free himself.
Although relaying this event to Chie and Yosuke the next day yet dismissing it as a dream, they head to Junes to see what will happen on a widescreen television.
Instead of being dead, Kurono finds himself trapped in a small apartment along with Kato, a bunch of weird people (including a hot naked girl, a dog, and a middle-school boy who seems to be the only one who knows what's going on) and a large black sphere.
The sphere sings an exercise song, and explains the situation: they were dead, but "Gantz" (which an experienced character says the sphere has just "always been called," not knowing where the name came from) needs them for the mission of killing a weird alien creature (the first of a series, as it turns out).