What is the background story of Mouse Brother Cao Yi?

In "Journey to the West", the background is that rats cultivate themselves into spirits. The mouse brother Cao Yi is a character in "Journey to the West", one of the four great wonders of ancient China. He is a mouse spirit transformed from pure yin energy. He has practiced for many years and developed the ability to subjugate demons and eliminate evil spirits. When he appeared on the stage, he fought with Sun Wukong, was defeated by Sun Wukong and was accepted as his subordinate. Later, he became one of the protectors of Monk Tang on his way to the West to learn Buddhist scriptures.