The protagonist and Midou Sayuri have been a couple for about a year. They get along well, and have sex quite often, but it's started to feel stale. One day, the two of them head to the usual love hotel, and do a raffle using the points they've saved up there. What they got from it was the "easy SM set" adult goods. "Hey, since we got it, we might as well use it. It'd be a waste to throw it out." Nodding at Sayuri's casual suggestion, they decided to use those adult goods. ...That's where the SM play between just the two of them begins.

[Translated from DMM]