My sister-in-law Yuriko suddenly came to live at my house after our parents remarried. Still at that age, she's just starting to become curious about sex. One day, she suddenly shows up in the bath, or sneaks into my bed and pokes, pokes, pokes at my dick. When I scold her, saying "No, this is wrong!", Yuriko goes back to her room and sadly masturbates alone, trying to endure it. But her desire keeps growing stronger, until finally she can't resist the urge to have sex any longer—and takes action. Unable to hold back myself, I eventually end up having sex with Yuriko...