Three years into their marriage, husband Yuji and his wife Erina are expecting their first child, and they move to their parents' home. Erika's father and older sister Yuka live there. Ever since Erika became pregnant, Yuji has been refusing sex, and it's made him feel even more aroused when he sees the kind and beautiful Yuka. Unable to bear just staring at Yuka with annoyed eyes, Yuji waits for an opportunity when Erika isn't around and pushes her down...