Hataraki Man(2006)

Hataraki Man

Hiroko Matsukata is a woman who works for a magazine company. She puts all she has into her work, and is known as a strong, straight-forward working girl, who can at will turn herself into Hataraki man (working man) mode. Despite Hiroko's success at work, her life lacks romance. Even though a hard worker, she'd leave early anytime to go on a date. Too bad her boyfriend is even bigger a workaholic than Hiroko.

(Source: Anime News Network)