In a near‑future world where tensions rise between Japan and China, humanity’s most celebrated achievement is the Ocean Techno Polis, a massive, floating, man‑made city above the sea. A mysterious catastrophe strikes when a Taiwanese submarine is destroyed, and within moments the entire city is plunged into the ocean. Kurase, one of the engineers of Ocean Techno Polis, races against time to rescue his family while confronting a Japanese navy that is hiding its own secrets. As he delves deeper, Kurase uncovers the true cause of the city’s downfall. The story is adapted from the 1995 novel by Katsufumi Umehara.