Fukurokudou Hirentan

En is a medicinal master who runs a Chinese Herbal Medicine shop with his apprentice, Tao. Despite being a well-sought medicine master, En tends to be lascivious and pleasures himself with the company of other men, much to the ire of Tao, who has feelings of attraction for his master and tries his best to hide it. Unfortunately for Tao, he isn't exactly subtle, and En knows about his infatuation. En then proceeds to tease his cute apprentice and propose that Tao be his bed partner instead.
(Source: Futekiya)