Gantz

Gantz is a sexually-charged sci-fi head-trip' a gory experiment in flesh and blood where the only thing worse than dying is dying again.
If you are chosen by the bizarre black sphere known as the Gantz, you are already dead. You remember dying, yet you can eat, sleep, have sex; it feels a lot like life. Strangers join you in this limbo. While some are good, some are very bad. All are dead like you for now.
You might be able to reclaim your mortality. But first, the Gantz demands that you undertake missions of brutality and madness, killing aliens hidden among the population. It is your only chance and you have no choice. You must play this disturbing game. You must experience this nightmare. And if you die again and you likely will it's permanent.