In 2157 AD, after experiencing the rise in sea levels caused by the greenhouse effect, the energy crisis, and the resulting World War III, the world's population has dropped sharply, and large areas of land have become uninhabitable due to the impact of nuclear radiation. Humanity was forced to disperse across previously inaccessible islands. It is precisely because of this that people ushered in another age of navigation: the Age of Discovery. And the legend of the sea gradually spread...