Gantz

Gantz is a black orb with a man inside of it in a locked room located in Japan. Usually up to ten people who die in unison appear there to be given a second, yet, impossible chance of life. Gantz is a supposed game and in order to win it you must do as it tells you. After being told your task, and after being given tools to perform it, you are sent to another part of the world to complete it. The task is revolved around killing an alien or aliens that can sometimes be impossible to kill without great skill. The more targets you kill, the more points you get that prepare you for the future. After completing your mission, if you're still alive, you are transported back to the room you were once in, your wounds are healed, and are told your score. If you eventually reach the mark 100 or + then "something" will happen. While in the mission zone, if you carelessly walk off then you will die of what seems to be an explosive in your head, and so fourth you loose the game. Also Gantz has given the ones who died in unison a second chance of life and can do whatever he wishes to you at that point, so a recommendation would be NOT to piss him off because he can manipulate the minds of others to, with all their heart, want to kill you.