My brother and his wife, my mother, and I went on a trip to a hot spring in the suburbs... and for some reason, I did. My sister-in-law, Nao, prepared two pairs of tickets, so I was forced to join them to make up the numbers. The inn was more luxurious than I expected, and my mother and brother were so excited that they quickly got drunk. While the rest of the family was asleep, I was left alone with my beautiful and kind sister-in-law... Her bare skin, reddened from the bath, was peeking out from under her yukata, and I couldn't take my eyes off her. Nao must have noticed my gaze because she came over to me...