Soliton no Akuma

In the future, tensions are rising between Japan and China. The jewel of humankind is the new Ocean Techno Polis, a man-made city which floats above the sea. One day, a mysterious catastrophe destroys a Taiwanese submarine followed by the entire city of Ocean Techno Polis. One of the engineers of Ocean Techno Polis, Kurase, must race to rescue his family. Along the way, he must deal with a Japanese navy trying to keep their own secrets under wraps, and discover why Ocean Techno Polis sank to the bottom of the sea.