My older sister, who lives alone in Tokyo, has come back to her parents' house for the first time in a while! My older sister is kind, smart, has big breasts, a nice figure, and is cute... in other words, she's my type. She always treats me like a child and wants to take a bath with me, saying, "I'll wash your back!" I can't help but be curious about my older sister's breasts when she forces me into the bath... and her big breasts keep touching my body, making me get an erection. Of course, my older sister finds out...