Gantz: O (styled as GANTZ:O) is a 2016 adult Japanese animated science fiction action film directed by Yasushi Kawamura and Keiichi Sato (chief), written by Tsutomu Kuroiwa, animated by Digital Frontier, and based on the manga series Gantz, which was written and illustrated by Hiroya Oku. It was released in Japan by Toho on October 14, 2016.

Plot

While fighting invading monsters, Kei Kurono rescues his friend, Reika. Though she protests, he attacks the monsters' leader, dying after killing it. Reika and her surviving teammates are teleported back to their base. Elsewhere, Masaru Kato dies attempting to save someone from a knife attack in a subway. He wakes up in a room with Reika and her teammates: Yoshikazu Suzuki, an old man; Joichiro Nishi, a surly teenager; and an angry, unidentified man. Suzuki explains that they have each died and woken in the room, and have been forced to fight against waves of monsters ever since. Before Suzuki can explain further, a black orb identified as "Gantz" announces that their next mission is about to begin. The angry man refuses to participate and is killed by Nishi, who reasons that he would have been a liability.