Chao is a young girl whose village was being terrorized by Terror and Plague.

Chao left her village to get the help of the Tiger Thief, only to be nearly killed by him, and then saved by Goku. Chao asked Goku to save her village because of his great strength. She brought Goku back to her village and they arrived right when the Terror was about to seal a baby called Chenshi in the Gourd of Mist, because he was two weeks old, and he could not say his name when called.

Although Goku, to disgusted by what they were planning to do to Chenshi, he confronted Terror and Plague, only to be absorbed by he gourd before he could damage them. However, he managed to jump out and defeated Terror and Plague, saving the village.

(Source: Dragon Ball Wikia)