This series is set on a fictional Mars, where, aside from the planet's highest peak, Olympus Mons, the entire surface is covered by water and ice. As a result, the people living on Mars have constructed "city ships" adapted to the Martian ocean environment. Due to Mars' abundant water resources, Earth's government views it as a strategic development base, but this has also drawn Mars into an interstellar war. Ravaged by the flames of war, Mars has fallen into unprecedented decline, with its people suffering greatly. Consequently, several groups of pirates and resistance forces have emerged to oppose the Earth government's oppression of the Martian inhabitants.