Zi Xuan is the disciple of the Green Emperor and he specializes in medicine and is cultivating to become a deity. He meets a little white snake, whom he nicknamed Xiao Bai, and kept as a pet. Over the course of time, Xiao Bai gathered enough cultivation to transform into a human, and she eventually grows closer to Zi Xuan and developed a close/intimate relationship with him. While trying to find a herb that would save Zi Xuan's life after he is injured, she accidentally breaks a heavenly seal at the elixir chamber of Mount Jiuxi and releases an ancient beast, the black water dragon from imprisonment to the human world. To save the world, Zi Xuan sacrifices himself and disintegrates, but before he fades, he gives Xiao Bai a proper name: Bai Yaoyao. After Zi Xuan's death, Bai Yaoyao is devastated and decides to retreat from the world. A thousand years pass by and they meet again. Zi Xuan, now reborn as Xu Xian, who is the chief of the Yao Shi Palace (medicine valley), remembers nothing of his and Bai YaoYao's past. However, she remembers everything and she tries to ensure that he lives a peaceful life.