The world has been overrun by a zombie apocalypse, and 22-year-old hikikomori Yuu Oikawa has been holed up in his apartment, resigned to a lonely death as his food runs out. In his final moments, he is visited by a woman named Sunny Aishu, a brilliant scientist who has developed a unique vaccine against the zombie virus. Unable to mass-produce it, she injects Yuu with the only dose, granting him a peculiar ability: by transferring his bodily fluids through sexual intercourse, he can revert zombies back to human form.

Armed with this power, Yuu ventures into the dangerous, zombie-filled world. He encounters other survivors, including a young woman named Kanae Sugawara, a former teacher Ayase Kouichi, and later a clingy, mysterious girl named Rio. Key narrative arcs include a tense standoff at a home center where a zombified high school student Noriko Shihoji threatens the survivors, forcing her teacher Kouichi to reluctantly ask Yuu to use his vaccine to save her. Later, Yuu and his group take refuge at a hot spring inn, only to be attacked again, and Rio’s hidden secrets begin to surface.

As Yuu continues his mission, he grapples with the ethical weight of his ability, the growing attachment from the women he saves, and the looming threat of Sunny’s own zombification after she was bitten. The story blends survival horror, dark comedy, and explicit adult content, with Yuu evolving from a withdrawn shut-in into a reluctant hero whose only hope for humanity rests on an intimate and controversial cure.