"Yīnyáng Xiānshēng" is the fourth song of the Didn't Eat Medicine Yet series and features Tianyi and YANHE. The song is about the master of Fengshui (Yin and Yang) (YANHE) giving a girl (Tianyi) some medicine to avoid the Night Crawler. At first the master asks for the girl to give him her hand to see what trigram she has, but the girl pushes him away and calls him a fraud before yelling for police to come. The master then says that from his knowledge, he observes that she cannot sleep at night for there is something hiding by her bed at night. At those words the girl realizes he is genuinely a master and begs for him to help her.
The master sings that he will do all he can to help her, also adding that Yin and Yang exist within him with the ability to solve many things.
He then proceeds to hand her a small statue that is supposed to keep away evil, but she laments that that wouldn't help her. Hearing this, he then hands her a bit of medicine, saying it will help cure her. As the day fades into evening, she thanks him and goes back home while he says that "we will meet again."
When it grows dark, all the pedestrians return home, and so the master also walks off. As he walks, he sings an odd song no one has heard of before which is the same name as the next song in the series, "Funeral Song".
This song was featured in the compilation album Diàntáng 2.
This song exceeded 100,000 views on bilibili. In June 2015, it reached 1 million views.