Yi Jian Shuang Han

The sickly Sect Master Yun Yifeng peddles intelligence, and Prince Xiao requires his service to investigate a theft. Enticing Yun with medicine that can cure his sickness—something Prince Xiao doesn't have—the two embark on a journey to investigate the theft. Something blossoms beyond friendship along the way.

(Source: Bilibili Comics)

Note: Chapter count includes an extra.