Yuki is a newly married housewife who has a secret she can't tell anyone about. It's an affair with her childhood friend. The two have been in love since before they got married. "He and I are Kokoro brother and sister," says Yuki. But it's just a "convenient sex friend" - she calls him to a hotel and does whatever she wants with him. They've been together for a long time, so they know exactly what makes them feel good. They engage in a variety of passionate sex acts that they would never do with their husbands or wives. A forbidden affair that burns because of the risks. A dangerous love is sweet.