Erika Arimura spends three days having sex in her older brother's room before her younger sister, a sexual monster who is going to a boarding school in the spring, moves out.

On the day my parents were away from home for a memorial service, I was alone with my younger sister who was about to move out... Seeing the defenseless appearance of my younger sister, who the family was proud of as being good at studying and cute... I couldn't resist my desire, so I forced myself. I end up raping my sister... Then, my younger sister told me that I might actually have stronger sexual desires than other people. From then on, I had sex with my sister over and over again until the day I left home to move... This is a record of that day.