The tranquil day was shattered by the unexpected arrival of extraterrestrial creatures known as the Unknown, who swiftly and mercilessly attacked humanity. In order to safeguard the nation's future, Japan's children were cryogenically preserved until the war's end to ensure their safety. After a few years, humanity had secured a tenuous hold on a small part of Japan, now the frontline of the ongoing conflict. With the youngsters finally awoken from their cryogenic sleep, it was discovered that each child had developed unique supernatural abilities known as Worlds. The six most dominant youngsters were appointed leaders of the reclaimed cities, utilizing their powers to guard against further invasion. Friends Ichiya Suzaku and Canaria Utara ruled Tokyo, siblings Kasumi and Asuha Chigusa controlled Chiba, while Maihime Tenkawa and Hotaru Rindou presided over Kanagawa. As time passed, the frequent assaults from the Unknown, as well as clashes between the city rulers and subordinates, bred petty rivalries, giving rise to incessant arguments between the three cities. With the Unknown intensifying their attacks, the leaders of the three cities must learn to work together or risk the final eradication of their already-weakened humanity.