Over time, there has been growing tension between Japan and China. The Ocean Techno Polis stands as a remarkable display of human innovation, a sprawling metropolis established on top of the sea. Regrettably, the Taiwanese submarine and the entire city are destroyed by an unexplained calamity. Kurase, an engineer hailing from the Ocean Techno Polis, rushes to save his loved ones, but encounters difficulties from the Japanese military as they are keen on keeping their classified data concealed from him. Furthermore, he must ascertain the reason why the cutting-edge city plunged into the depths of the ocean.