Koi Saki, a lustful, voluptuous woman with a highly sensitive body, plunges into a mixed-gender hot spring. The hot spring, which springs from the riverbank, does not have a changing room. As she spreads her legs in an M-shape or gets on all fours and spreads her slit, her breathing gets rougher and rougher. She becomes more and more immersed in the pleasure of being watched, and writhes in pleasure, showing the man glimpses of her private parts...