Season 1

Hibiki Mamiya, an auto mechanic living at the southern tip of the Miura Peninsula, is an upright and trustworthy man who plans to propose to his girlfriend, Kurumi—an intern doctor with whom he lives. While on his way to work, Hibiki becomes trapped following a mysterious tunnel collapse. When he finally escapes the tunnel days later, he is confronted by a chilling, desolate, and deserted cityscape.

Hibiki, who had survived the journey to the U.S., headed for the intersection, only to find an abandoned, driverless bus surrounded by the carcasses of monsters. While Todoroki and his group protected Hibiki as he attempted to repair a nearby vehicle—fending off attacks from other monsters—and Hongo and Komoto set out to scavenge for gasoline, Masaomi Uwajima was concealing a terrifying transformation.

Upon arriving at the Self-Defense Force base—intended to be a sanctuary—Hibiki and the others came under sudden gunfire; leaving behind Daiki Hongo, who had been shot and collapsed, the group risked their lives to flee the scene. However, false reports circulated within the Self-Defense Force claiming that Hibiki’s group had fired first, leading to them being branded as terrorists. Three days later, the group was hiding from swarms of monsters that turned ferocious at night...

To rescue Kanae, who was being held hostage, Hibiki and his group surrendered to the "Sword Group" and were taken to the shopping mall's underground level, where a large number of "Ghouls" were being held captive. Tsuboi, the leader of the Sword Group, intended to break the agreement and kill Hibiki; meanwhile, Kurumi arrived at the same mall with the Self-Defense Forces in search of Hibiki. The Sword Group abducted her when she was left alone, causing her to narrowly miss crossing paths with Hibiki.

To save Yuzuki, who is suffering from an asthma attack, Hibiki and the others risk venturing out to find medication. They sneak into a hospital, only to discover that the medicine has apparently been cleared out. Hibiki leaves the rest of the group on the safety boat and heads to another hospital with Min-jun; along the way, they rescue survivors surrounded by monsters—including Shozo’s husband, Komae, who had rushed in from outside the blockade in search of his wife.

In search of medical supplies, Hibiki and the others decide to approach the base by sea; however, while stopping at a small island along the way, they encounter Tsuboi’s group—members of a faction that had previously been hostile toward them. Inside the isolated base, a conflict of opinion arises between Self-Defense Force Commander Kojiro Ushigome, who advocates for withdrawal, and Shuto, who insists on developing the vaccine right there at the base...

Hibiki encountered his mother, Kinko—whom he had believed to be dead from illness. Although shocked by her altered appearance, he quietly walked away without making a move toward her. Meanwhile, Kanae and Min-jun, who were worried about Hibiki, met up with Kurumi and Shori. Believing that his sister had been killed by "terrorists," Shori attacked Min-jun, while Kurumi pointed her knife at Min-jun to protect Shori.

Upon learning the reason Min-jun was bitten by the "monster," his companions are driven by a desire for revenge over his loss. As the number of survivors at the base dwindles, Ji-an—who has turned against Shuto—discovers that the cryogenic unit does not contain the vaccine; instead, it is stored in a different room within the base. Amidst this situation, the Self-Defense Force personnel stationed there begin scouting areas outside the base in search of a safe location.

The person Hibiki struck with an arrow turned out to be Kurumi; the shock left him momentarily speechless, while the unconscious Kurumi faced a critical situation. Back at the base, An—who was under the surveillance of Shuto—grew suspicious about the true nature of the "vaccine" Shuto was administering to the refugees.

It turned out that the person pointing a gun at Hibiki was Kurumi; even more shocking was the fact that people at the base were turning into monsters one after another. Hibiki was devastated when Kurumi fled back to Shuto. Thanks to the antibiotics Hibiki and the others brought back, Shoji was able to get back on her feet, while Kuwata began to realize just how terrifying the "vaccine" Shuto had created truly was.