Game: Between the Suits Vol. 5 (manga)

At twenty-seven, Sayo is married to her career–she's the kind of woman who will even answer work calls while having sex! When her firm hires charming playboy Ryoichi, Sayo tries to resist his advances, but not for long. Soon they're plunging into a purely physical relationship, agreeing that they'll only play this love game until they find true romance. Sayo will let Ryoichi into her bed, but will she let him into her heart...?