Returning home for the summer, Jiro comes back to his family house and learns his brother and sister-in-law are undergoing infertility treatment, leaving him with an odd sense of unease amid the seemingly ordinary family life. That night, by chance, Jiro peeks into his brother's room and is stunned to see his demure sister-in-law Kana behaving in a wildly passionate manner, completely unlike her usual calm self. Kana's intense desire manifests as she demands creampie sex from Jiro once his wife enters the stable phase of pregnancy. Sneaking away from the family's watchful eyes, the sweaty, aggressive Kana relentlessly pushes Jiro to climax, and he finally gives in, shooting his load deep inside her vagina. On this night where family secrets and desires collide, Jiro takes a new step in his relationship with his sister-in-law.