小野大輔
is one of the two main protagonists of the series. He is summoned, along with Kurono, by Gantz after they were hit by a subway train while helping an unconscious hobo who fell on the tracks. He is a childhood friend of Kurono and serves as a secondary protagonist. At school, he acts as a guardian to the weaker students who often find themselves bullied, getting himself a bit of a reputation for fighting. He initially lives with an aunt who reluctantly adopted him and his brother after they were orphaned. They leave after Kato saved enough money to rent an apartment room for both of them; in the anime version, they moved after he could no longer stand their aunt hitting his little brother. He is killed during the Thousand Arms mission. He is later revived near the end of Phase 1 by Yoshikazu Suzuki who asked Kurono who he wanted to revive. After that, he manages to kill Nurarihyon and gains 100 points, choosing to revive Kurono. In the Japanese series, Kato is voiced by Masashi Oosato and by Daisuke Ono in Gantz: O. In the anime English dub is voiced by Illich Guardiola. In the live-action movie, Kato is played by Ken'ichi Matsuyama.