On a tranquil day, the skies tear open, and extradimensional entities known as the Unknown launch a swift, brutal assault on humanity. To safeguard the nation's future, all of Japan's children are cryogenically frozen until the war's end, keeping them safe from harm. Years later, humanity has secured a foothold in a corner of Japan, which now serves as the war's frontline. With extinction no longer imminent, the children are awakened from their slumber. It is then revealed that, during cryogenesis, they developed Worlds—supernatural powers unique to each individual. The six most powerful children are given command of the reclaimed cities, using their abilities to defend the strongholds against the ongoing invasion. Childhood friends Ichiya Suzaku and Canaria Utara lead Tokyo, siblings Kasumi and Asuha Chigusa manage Chiba, and Maihime Tenkawa and Hotaru Rindou oversee Kanagawa. Over time, the near-routine attacks by the Unknown and the clashing personalities of the city leaders and sub-leaders foster petty rivalries, resulting in constant arguments among the three cities. As the Unknown suddenly intensifies their assault, the leaders of the three cities must learn to cooperate or risk losing humanity's last line of defense against extinction.