A special collaboration between S1 exclusive G-cup beauty "Tsubasa Mai" and Madonna for the 20th anniversary!! Mai and I are not actually siblings. When I was a student, my mother remarried and my sister Mai was her stepdaughter. After my parents fell ill, Mai became my parent figure. As we spent more time together, I gradually began to fall in love with her. One day, I invited my classmate Yuzuru over to my house for a meeting about the school festival. Yuzuru seemed interested in Mai, whom he had met for the first time, and from that day on he started coming over to my house frequently...