After many centuries of disciplined training in Taoism whilst living in a cave on Mount Emei, the protagonist Bai Su Zhen, with the help of a heavenly immortality pill, transforms herself from her original form as a snake into human form, en route to seek immortality on her quest for divinity, guided by the Mother of Mercy, Guan Yin. She then meets and defeats Xiao Qing ("Small Green") in combat, and chose mercy rather than ending Xiao Qing’s life. Xiao Qing then transforms into a female maiden and swears her loyalty as Bai’s servant in return for sparing her life (though they become close like sisters). Xiao Qing, like Bai, had originally been a serpent.