A few months ago, Shota's mother remarried. Her new wife had a daughter, Hibiki, with her previous wife. Shota fell in love with his new sister-in-law Hibiki's huge breasts at first sight, and he started planning to play pranks on her by squeezing them. He takes full advantage of the privileges of having a small child that everyone envies, and does whatever he wants with his big-breasted sister-in-law!