Otona no Yoru no Otogibanashi(2007)

Otona no Yoru no Otogibanashi

As Asuka dreams of marrying a wealthy man, she has polished both the appearance and mind. Now it is rumored that she is the coolest beauty in the secretary division of the company. However, one of her friends ran away with the elite who she wished to marry.

She had a drink in desperation, and slept with Yuki, a nephew of the president of the company. Meanwhile, Yuki is assigned to the secretary division, and the delicate relationship between him and Asuka begins. Asuka who is naive, though she is a capable woman, and Yuki who is capable, though he is a greenhorn, develop a sweet love in a mature way.

(Source: Shoujo Manga Maniac)