Nao and I are not real siblings. Nao was the stepchild of her father who remarried when she was a student. After that, Nao, who was a year away from her parents' death in an accident, took the place of my parents. Life with them was lonely, but I was happy because I was in love with Nao. One day, her best friend Yuzuru was talking to Nao sister, and when she approached while remembering her jealousy, she was well distracted. And at some point, Nao's sister is often late for her return ...