Gantz is a Japanese manga series written and illustrated by Hiroya Oku. The story revolves around Kei Kurono and Masaru Kato, who find themselves involved in a deadly game orchestrated by a mysterious black sphere known as Gantz. The series combines elements of science fiction, horror, and action, exploring themes of life, death, and morality. Gantz has been adapted into various formats, including anime, films, and video games.