Kusakabe Kachou no Koi wa Yawaraka

Sana, self-conscious about her weight, is confused by her manager Mr. Kusakabe's constant glare. One day, she slips on the stairs, but Mr. Kusakabe catches her, and her embarrassment grows, certain he now thinks she's heavy. But when she confronts him about his stares, he blushes and confesses his love, revealing his "glaring" was actually a sign of affection. He then asks her on a date in this cute office romance.

(Source: MangaPlaza)