My brother and his wife, my mother, and I, for some reason, came to a hot spring trip in the suburbs. Her sister-in-law, Nao, prepared tickets for two pairs, so she was forced to participate in the matching. The inn was more luxurious than expected, and my mother and brother were so excited that they quickly passed out after drinking alcohol. While my family was asleep, I was alone with my beautiful and kind sister-in-law... After bathing, my bare skin turns red and peeks out from under my yukata, and I stare at it.