I'm a college student, and I was invited to my girlfriend's house for the first time in my life, and I was introduced to her younger sister, Emi. At first glance, Emi seems plain and serious, but she seems shy and reads books quietly and says little. I was looking forward to her cooking, and then suddenly, Emi appeared, pressed her body against mine, whispered in my ear, "Have you ever had sex?" and slid her hand between my legs. Then, she smiled as if toying with me, and started to show me her lewd nature while repeatedly saying obscene things...