Ms. Ironheart's Illusive Smile

Kokoro Kurogane is a beautiful and hard-working perfectionist known for her icy personality. Always arriving at the exact same time every morning and completely dedicating herself to her work, she is admired... no, rather feared, in the office.

One day, a handsome heartthrob, called Tohno Takaomi, transfers to the office after working abroad in America. He is intrigued by Kokoro, who is secretly known as the "strict" and "impossible to read" "Ms. Ironheart" by her colleagues. He tries to get close to her, despite the barriers she's put in place, but this unexpected attention is throwing her perfect system out of whack!

(Source: MangaPlaza)