GANTZ is a Japanese manga and anime series created by Hiroya Oku. It follows the story of Kei Kurono and Masaru Kato, who are resurrected by a mysterious black sphere known as Gantz after dying in a train accident. The duo, along with others in similar situations, are forced to participate in missions against aliens and other supernatural threats. The series explores themes of life, death, and morality, blending science fiction with action and horror elements.