Magari Kado no Kanojo.

33-year old Oshima Chiharu is a career woman in the Sales and Planning Department of a hotel. During her 20's, Chiharu worked day and night to achieve her current position and luxurious lifestyle. She won't let anybody interfere with her career and romance. All is going well, until 25-year-old Mihara Natsumi throws down the gauntlet to Chiharu. Everybody including Chiharu had thought that Natsumi was just a girl with no brains. But actually, once she sets her mind to something, she can achieve anything. She is good at learning foreign languages, and is prepared to use her sex appeal to entrap and exploit men. What's more, since Natsumi was brought up in a poor fatherless home, her desire to climb the ladder of success is strong. She knows that the only way she'll get a chance is to outperform Chiharu and snatch away her post. That's exactly what Natsumi decides to do