Nao and I are not real siblings. Nao was the child of the other person whose father remarried when he was a student. After that, my sister Nao, who was a year away from my parents' death in an accident, was my parent. Life with them was lonely, but I was happy because I was in love with Nao. One day, my best friend Yuzuru was talking to Nao sister, and when I approached him with jealousy, I was confused. And at some point, Nao's sister is often late to return ...