Kemuri no Saki no Shikishima-san

A romantic comedy about the secret interaction between Koda, a company employee, and Shikishima-san, the madonna of his workplace. Shikishima-san always wears a mask and rarely has a chance to take it off, and it is said that no one knows her true face. However, Shikishima is a smoker and Koda, who meets her in the smoking area, is the only one who knows Shikishima's true face.

(Source: Shonengahosha, translated)