I was thinking about marrying my girlfriend, who I was living with. She has a younger sister. Her name is Rin... She is friendly, already calls me her big brother, and talks to me in a friendly manner. One rainy day, Rin came to my house soaking wet for refuge. ...A big lightning strike caused a power outage, and the moment I touched Rin's body as she embraced me, my reason was blown away and we had raw sex...Even though I felt a sense of guilt, we made love in the bath, after dinner, and many times until the morning...