On a midsummer day, when the heat was constant, my kind sister-in-law, who couldn't help but feel uncomfortable with me, who was in trouble because my wife was bedridden with a summer cold, came to help with housework. Furthermore, coincidences have come together, and sister-in-law Rin, who works overseas, has returned to Japan for a while. Then, a strange life begins at my wife's parents' house with two step-sisters with breasts that are so big that it can't be compared to her small-breasted wife. Just because I was contagiously suffering from a cold, I ended up sleeping with my two sisters-in-law in a river, and I couldn't sleep because my breasts were tightly attached to me from both sides...