This is Mars where the surface is covered with ices and oceans. Therefore, people built a "City Ship" to live. It is a large submarine and it can move slowly. Because the water on Mars was important resource of energy, the Mars was the strong point of water resource for the Earth government. After that, the galaxy scale war broke out. The Earth was also involved the war. Because of the special demand for the war, Marian economy grew. However, after the war ended, in addition to postwar confusion and the oppression of the government, the Martian economy was suffered from big slump.
The complaints of the Martian grew, and the rebellion took place in various places. The independent movement got into stride.
Furthermore, pirates grew in number to attack the military facilities. The Earth government organized the military unit for the Mars, and began to suppress the independent activities and the pirates.