Kazumi, who lives alone, receives a wedding invitation from a friend. She wears the dress she recently bought for the occasion, but the zipper gets stuck around her butt. In a pinch, Kazumi decides to go to the gym before the wedding to tone her butt so she can wear the dress she bought. Kazumi tries all kinds of exercises, using a yoga mat, balance ball, etc. However, her bold hip movements, not caring about the people around her, unconsciously seduce the young instructor...