MIAA-384 [Uncensored Leaked] Sudden heavy rain caused a refugee situation and my girlfriend's sister and I stayed up until the morning... Kira Rin

I was thinking about marrying my girlfriend, with whom I was living together. She has a younger sister. Her name is Rin... She's friendly, already calls me big brother, and talks to me in a friendly manner. One rainy day, Rin came to my house soaking wet for shelter. A large lightning strike caused a power outage, and the moment Rin embraced me and I touched her body, I lost all reason and we had raw sex... Despite feeling a sense of guilt, we continued to make love in the bath, after dinner, and until the morning came...