Gantz/24 by Hiroya Oku

Set in a world where the boundaries between life and death blur, the story follows a group of individuals who are resurrected after dying, only to find themselves part of a mysterious game orchestrated by a black sphere known as Gantz. These individuals are tasked with hunting down and eliminating alien threats, each mission more dangerous than the last. As they navigate this perilous new existence, they grapple with their own personal demons and the moral complexities of their actions, all while trying to uncover the true purpose behind their resurrection and the enigmatic Gantz.