Nao-nee and I are not real siblings. When she was a student, her father remarried and her stepchild was Nao-nee. Later, after my girlfriend's parents died in an accident, Nao-nee, who was a lot older than me, became my parent. Living together was lonely, but I also felt happy because I was in love with Nao-nee. One day, Nao's best friend, Yuzuru, was secretly talking to Nao-nee and approached her, feeling jealous of her.