Gantz

In a nondescript room in Tokyo, a mysterious black sphere lies in wait. It periodically summons individuals who have narrowly escaped death, equipping them with high-tech suits and deadly weaponry before dispatching them on perilous missions to hunt down and eliminate beings from another world that have invaded Earth. The participants, unaware of the larger world's ignorance of their activities, are forced to navigate these lethal assignments, with the sphere pulling the strings and meting out merciless justice to those who fail to comply. This enigmatic entity, known as Gantz, exercises absolute control over the lives of those it has chosen, with survival a distant hope in a desperate game of survival.