I live with my brother and his wife. I'm always comforted by my sister Shiho Shiho's kind smile. One day, my brother goes on a business trip, and I'm left alone at home with my sister- in-Shiho. That's when our naughty relationship began... She purposely comes in while I'm taking a bath, changes her clothes in front of me, and finally we sleep in the same bed... Our forbidden relationship, which we keep secret from my brother, continues to this day...