Sotomura Tanteisha no Manekarezaru Kyaku

Kei Matsuda is a private investigator who specializes in quirky cases centered on his local neighborhood around the shopping arcade. He's recently taken on a new roommate (and lover) named Kamiko who is unemployed, ruthlessly horny, and was actually a classmate from his past.

While the two work together to solve cases, they carry on in what starts as a strictly physical relationship... until Matsuda finds that this temporary situation he has entered with Kamiko might be turning into something more.

(Source: Tokyopop)