That JAV

My sister Nao and I are not really sisters and brothers. When I was a student, my father remarried and my sister Nao was his stepdaughter. After my parents died in an accident, my older sister Nao took the place of my parents. I felt lonely living with her, but I was also happy because I was in love with her. One day, my best friend Yugen was secretly talking with my sister, and I approached him with jealousy. Then one day, Nao's sister started coming home late...