Yes, this was the plot of the book,"Spoiling the Peerless Attendant." The author was Shushu Cat. It was a fantasy romance novel. The protagonist befriended his brothers in the noble academy, subdued the divine herb, learned medicine, and became a peerless errand boy. The process of being taken in as a son by the male protagonist was quite interesting. I hope you like this fairy's recommendation. Muah ~π