Katsunori Hamuro belongs to the Gallients, a faction of former convicts under Renjiro Hatonami's leadership. Previously a fisherman, he was imprisoned after killing a friend during a violent altercation. He escaped incarceration during the Gibia virus outbreak and aligned with the Gallients.

Physically robust with black hair and grey eyes, Katsunori conceals most of his face with a scarf and bears a sword on his back. His fishing background directly shapes his combat techniques: he captures Gibia by casting nets, hooks them with a fishing rod, and wields his blade with proficiency.

Within the Gallients, Katsunori engages in collective survival efforts like scavenging for resources and clashing with rival survivors. During a critical food shortage, the group ambushes Sensui Kanzaki’s team, taking Kathleen Funada hostage to extort supplies. After Renjiro falls to Sensui, Katsunori volunteers to challenge him but is overruled by Guren Soshigaya’s retreat order. The Gallients later witness Sensui’s group battling Gibia in a tunnel, acknowledging their skill.

When another supply mission fails, the Gallients prepare to confront Sensui’s group again. Mid-engagement, the powerful entity Meteora assaults both factions. Sensui’s group rescues the Gallients, forging a temporary alliance against this shared threat.