Masaru Kato, a kind-hearted teenager, is killed while attempting to protect others during a subway stabbing incident. He awakens in a mysterious room alongside a group of strangers, all facing a giant black sphere known as Gantz. They are informed that their lives have been "taken" and they must participate in a deadly game. To earn their freedom or resurrect a fallen comrade, they are tasked with hunting down
extraterrestrial monsters in a simulated version of Osaka.Unlike his counterparts, Kato is driven by a desperate desire to return home to his
younger brother, who is now orphaned. As the team is transported to the neon-lit streets of Osaka, they discover that the monsters they face are far more formidable than those encountered in previous missions. The city is overrun by grotesque, mythological entities, including the terrifying Nurarihyon, a shapeshifting boss with multiple transformations that prove nearly impossible to defeat.The Osaka team, veterans of these games, initially dismiss the newcomers, but they are quickly decimated by the sheer power of the monsters. Kato steps up as a reluctant leader, prioritizing the survival of civilians over the selfish point-gathering tactics of the other players. His unwavering morality clashes with the cynicism of the Osaka fighters, who treat the slaughter as a sport. As the battle intensifies, the true nature of the mission is revealed: it is not merely a game, but a brutal test of endurance.The climax erupts in a visceral showdown against the Nurarihyon. One by one, the strongest warriors fall, leaving Kato to face the final, god-like entity. Utilizing his remaining strength and the advanced weaponry provided by Gantz, Kato engages in a high-stakes duel. He manages to defeat the boss, but at a heavy cost, sacrificing his own safety to ensure the survival of his teammates. In the aftermath, the survivors are granted points, and Kato chooses to use his reward to resurrect a comrade, ultimately securing his own return to the real world. His journey transforms him from a victim of circumstance into a selfless hero who defies the cruel logic of the game, proving that humanity can persist even in the face of impossible, otherworldly odds.