Ayumu Katou

Ayumu is affectionate, earnest and strongly attached to his older brother. Their difficult home circumstances make him conscious of money and responsibility at an unusually young age.

He does not want Masaru to shoulder every burden alone. Even though he is only twelve, Ayumu talks about finding work himself so that he can contribute toward rent, reflecting both his maturity and his awareness of how hard his brother works for him.

His dependence on Masaru is emotional as well as practical. When his brother disappears during Gantz missions, Ayumu has no way to understand where he has gone and can only wait or search for him.

Ayumu is an ordinary human and never becomes a Gantz hunter. He has no supernatural abilities and does not use Gantz equipment.

His importance to the story comes from his place in Masaru's ordinary life rather than combat. Masaru's responsibility for Ayumu repeatedly influences how he thinks about survival, leadership and returning safely from missions.

Ayumu establishes the responsibilities waiting for Masaru outside Gantz. After their parents' deaths, the brothers live with Chikako Matsura and her family, but Masaru eventually works toward moving out so that Ayumu can escape their aunt's mistreatment.

After Masaru is killed during the Buddhist Temple mission, Ayumu spends months without knowing what happened to his brother. When Masaru is eventually revived, one of his immediate priorities is finding Ayumu and rebuilding their life together.

During the Katastrophe, Masaru's determination to protect Ayumu remains central even as the Gantz conflict expands into a worldwide alien invasion.

Masaru Katou is Ayumu's older brother, guardian and most important family relationship. Ayumu loves Masaru Katou deeply and wants to contribute financially rather than leaving every responsibility to him.

Chikako Matsura is Ayumu's aunt. Her harsh treatment of the brothers, particularly Ayumu, strengthens Masaru's determination to establish an independent home for them.