A zombie apocalypse erupts without warning during a high school festival. Koutarou Kosaka, a quiet otaku who loves shogi and video games, suddenly finds himself in a nightmare. He manages to pull a beautiful and outgoing classmate named Kana away from a swarm of infected. They take refuge in the gym, but Kana has already been bitten. Terrified of turning into a zombie before losing her virginity, she asks Koutarou to sleep with her. He agrees, and after their encounter something miraculous happens: Kana’s bite mark begins to disappear. They realize that Koutarou’s body produces antibodies during sex, effectively creating a cure for the zombie virus. Convinced this power can be used to save others and build a new life, Kana insists they stick together and have plenty of fun along the way.

Koutarou and Kana set out to find other survivors and expand their group. They head to a nearby all-girls school where many students have barricaded themselves. But the school is ruled by a tyrannical “King” who controls both the girls and the surrounding zombies through sheer force. When Koutarou refuses to submit, the King expels them from the safety of the school, forcing the pair back into the dangerous outside world. There they encounter a bubbly, wealthy young woman who is intensely curious about erotic experiences and eager to join Koutarou’s harem. After winning her over, the trio returns to the girls’ school and systematically dismantles the King’s harem, recruiting more former captives into their group. Their success, however, triggers a massive wave of mutated zombies that threaten to overrun the school.

The story then moves to new locations and challenges. Koutarou’s group rescues a nurse named Emma, who later leads them to a shelter where her colleague Rika is already infected. Just as hope falters, a mysterious figure known as “God” appears from the zombie‑infested Ikebukuro district. God reveals a personal grudge against Koutarou and proposes a one‑on‑one confrontation. Meanwhile, a rogue squad of gal cops captures Koutarou for unknown purposes, and other harem‑building factions emerge. The narrative escalates into a full‑scale conflict for dominance over the undead city, with Koutarou’s antibody‑making ability as the ultimate prize. As the Ikebukuro Zombieland arc reaches its climax, both sides unleash secret weapons, and the question becomes who will emerge as the true harem king in this chaotic, erotic, and darkly comedic survival story.