"Gantz: The First Stage" is a science fiction anime series based on the manga by Hiroya Oku. The narrative begins with Kei Kurono and Masaru Kato, two high school classmates who are killed in a train accident while attempting to save a homeless man. Instead of experiencing death, they awaken in a mysterious apartment room dominated by a large black sphere known as Gantz. Alongside other recently deceased individuals, they are forced to participate in a deadly game orchestrated by Gantz, which tasks them with hunting and eliminating alien targets within a time limit.

Gantz provides the participants with advanced weaponry, suits that enhance physical abilities, and instructions for their missions. Failure to complete the missions results in death, while success grants points that can be used to revive fallen teammates, gain freedom, or acquire powerful weapons. The missions are increasingly perilous, pitting the group against grotesque and highly dangerous aliens in urban and rural settings. The psychological toll of these missions is immense, as the characters grapple with fear, morality, and the value of human life.

Kei Kurono emerges as a central figure, initially portrayed as selfish and cynical but gradually developing a sense of responsibility and leadership. Masaru Kato, his compassionate and morally grounded counterpart, serves as a foil to Kei, often prioritizing the safety of others over his own survival. Other key characters include Kishimoto, a high school girl who forms a bond with Kei, and Nishi, a ruthless and enigmatic participant who prioritizes self-preservation. The dynamics between the characters are complex, with alliances and rivalries shifting as the missions progress.

The series explores themes of survival, existentialism, and the dehumanizing effects of violence. The missions grow increasingly brutal, with high stakes and frequent casualties, forcing the characters to confront their own mortality and the ethical implications of their actions. The narrative is punctuated by moments of intense action, psychological tension, and moral ambiguity, creating a bleak and unpredictable atmosphere.

"Gantz: The First Stage" concludes with an open-ended resolution, leaving many questions unanswered and setting the stage for further developments in the story. The series is notable for its graphic violence, mature themes, and unflinching portrayal of the darker aspects of human nature, making it a distinctive entry in the science fiction genre.