One hot summer day, a son-in-law moves into his wife's parents' home, beginning life under the same roof as his in-laws. However, as days pass, he finds himself increasingly drawn to his mother-in-law, Kyoko Shimada, and her soft, alluring body. Captivated by her charm, their relationship gradually deepens. Seizing the chance when his wife and father-in-law are away, the two find themselves alone together, and their bond transforms into something far more intimate. Slowly but surely, their forbidden connection begins to tie their hearts together.