I grew up in the countryside, but I went to Tokyo to attend a prep school, so I decided to stay with my older brother and his wife. However, my brother had to go on a business trip suddenly, and I was left alone with my sister-in-law, Tsubasa. My sister-in-law treated me just like she did when we were kids, but she was too defenseless... and it was too much stimulation for me, a virgin.