Gu Yun is described as good-looking, with peach blossom eyes. He has 2 cinnabar-colored beauty marks, one at the lower corner of his eye and another on his earlobe, the color of these marks fade and intensify depending on his medicine's efficacy. He sometimes wears a monocle made from liuli glass with a white gold chain attached to it that hangs behind his ear. Gu Yun is shown to be sarcastic, carefree, and straight-forward, saying what's on his mind in front of others.