Bijin na Jun-kun no Dekiai Shidou

When an annoying guy at work mocks her lack of femininity, Shoko gets dead drunk and begs for help from Jun, a boy at the bar whose beauty could outshine any girl, until she's talked him into coaching her on how to power up her feminine side. But Jun gives her two conditions: she has to live with him, and he gets to touch her breasts... This beautiful younger man's super erotic touchy-feely coaching is steadily training my body!

(Source: NTT Solmare Corporation, translated)