Jimi Joshi x Osekkai Danshi

Sudai Takashi is an employee of a candy company. After three years, he is promoted together with his new co-worker Kobayashi Chikako. Kobayashi is a person who is not sociable, is dull and shy. She also hides her chest since that caused her some problems in the past. Sudai will try to change this negative girl, and maybe he will start to harbour some feelings for her along the way.

Pixiv pre-serialization: https://www.pixiv.net/user/7764805/series/21243