Gantz (2004)
Plot
A group of people are brought back from the dead and forced to fight to have their lives back from a black ominous sphere named GANTZ. GANTZ wants them to kill a group of alien criminals that are hiding on Earth and it truly is a hopeless mission. If you die again...you won’t be lucky enough to have another chance to reclaim your life, but you don’t have a choice–you must take on the mission.
Where to watch Gantz?
Gantz is an action show featuring Daisuke Namikawa and created by Hiroya Oku.
Gantz is currently streaming for free (ad-supported) on Crunchyroll and it's also available on Crunchyroll.
It is also possible to buy Gantz on Amazon Video.