Thirty-five-year-old Hideo Suzuki works as an assistant to a successful manga artist, a dead-end job that barely pays the bills and leaves his own creative ambitions perpetually unfulfilled. Plagued by low self-esteem and unsettling hallucinations of floating faces and body parts, Hideo sees himself as a supporting character in his own life, a loser destined to remain on the margins. He finds small solace in his hobby of target shooting with a legally owned sporting shotgun, a skill that seems useless until the world collapses around him. The outbreak of a mysterious virus, nicknamed ZQN, sweeps through Tokyo, transforming the infected into aggressive, super-strong homicidal maniacs who repeat fragmented phrases from their former lives. After a desperate and traumatic confrontation with his own zombified girlfriend, Hideo flees the burning city, armed with his shotgun and a barely contained panic.

Hideo escapes the initial chaos and finds himself in the forest near Mount Fuji, where he encounters a quiet and empathetic high school girl named Hiromi Hayakari. Unlike the full-blown infected, Hiromi was bitten by a zombified infant without teeth, leaving her infected but still human, a unique condition that makes her a potential key to understanding the disease. Together, they join a small group of survivors taking refuge on the roof of a shopping mall. Among them is Yabu, a pragmatic former nurse who has been coerced into a horrific role as a sex slave by the male survivors now in charge. Recognizing the scientific significance of Hiromi's partial immunity, Yabu sees her as a chance at redemption and a cure. The fragile peace at the mall shatters when the surrounding ZQN horde breaches their defenses, forcing Hideo, Hiromi, and Yabu to make a violent escape. It is in this crucible of blood and terror that Hideo finally overcomes his crippling fear, using his shotgun with lethal precision to protect the women, violently shedding his passive nature for the first time.

As the trio continues their desperate journey, the narrative focuses on Hideo’s reluctant transformation. He is not a traditional hero; he is neurotic, indecisive, and haunted by the faces of those he has failed to save. Yet, his will to protect Hiromi becomes an obsession. The film builds toward a chaotic and gore-drenched climax inside a massive, zombie-infested warehouse. Separated from Yabu and cornered by a relentless tide of ZQN, Hideo makes a final stand. Unleashing a non-stop barrage of shotgun fire, he single-handedly holds back the apocalypse, blowing apart dozens of infected in a spectacular display of visceral action as he fights his way to Hiromi. The film ends on an ambiguous note, with the three battered survivors driving away into the wasteland, their destination unknown but their bond forged in fire. Hideo, the supporting character who could not even sell a manga, has finally performed the one heroic act that matters: surviving.