A floating city designed to be humanity's future sinks into the ocean in minutes, taking thousands with it. Kurase, one of the engineers who helped build Ocean Techno Polis, finds himself stranded on the surface with a single mission: find his family before they drown. But the Japanese navy has other priorities. They're actively suppressing evidence, stonewalling rescue efforts, and treating the disaster like a military secret rather than a human catastrophe. As Kurase pushes deeper into the wreckage and bureaucratic resistance, he uncovers the truth behind the catastrophe, one that implicates powers far beyond a simple structural failure. Geopolitical tensions between Japan and China simmer beneath every interaction, adding another layer of danger to his desperate search. What begins as a race against time transforms into something far more sinister, where survival means confronting forces that would rather keep the city's secrets buried at the bottom of the sea.