Celestial Warriors (Shichi Seishi) also known as Seven Star Warriors refers to the 28 servants of the four gods who guard a nation. Each god divided up the sky into four equal quadrants, and the twenty-eight warriors are divided into seven.
Explanation and Mythology
It was believed in ancient China that a heavenly king ruled the sky. There are 28 "star houses" which run the circumference of the sky ("Star House" is the Chinese term for "constellation"), located on the plane of the ecliptic (i.e. The plane running between the sun and Earth as it traces its orbit.) The heavenly king divided the sky into the northern, southern, eastern, and western quadrants, with each quadrant ruled over by a beast god. This belief was later adopted by ancient Japan. The 28 constellations were assigned by the ancient Chinese which run around the plane of the ecliptic in the night sky. If you think of the sky being ruled by a heavenly king, there are 28 star houses located around him. They were originally born to point out the areas above the heavenly sphere of the moon.
The heavenly king divided the sky into four groups of 7 constellations, with each quadrant controlled by a beast god. These deities are know as the Four Gods. Each god guarded their respective region of the Earth(north, south, east, or west) and each region had its own set of 7 constellations which the god ruled over. In addition, each god was associated with a specific season, element, and planet as well as its own important traits and significance to the planet.
Ancient Chinese astronomers divided the sky ecliptic into four regions, each assigned a mysterious animal. They are Azure Dragon (青龍) on the east, Black Tortoise (玄武) on the north, White Tiger (白虎) on the west, and Vermilion Bird (朱雀) on the south. Each region contains seven mansions, making a total of 28 mansions. The mansions or xiù are latitudes the Moon crosses during its monthly journey around Earth and serve as a way to track the Moon's progress. A similar system is used in Hindu astronomy.