My beloved sister-in-law, who raised me alone, was cheated on by my worst friend...

Nao-nee and I are not real siblings. When I was a student, the stepchild of my father remarried was Nao-nee. Later, after my parents died in an accident, Nao-san, who was older than me, was my parents. Although I was lonely with my life together, I was also happy as I was in love with Nao-nee. One day, her best friend Yuzuru was secretly talking to Nao-nee, and when she got jealous, she approached her and was successfully laid off. And then, one day, Nao-nee often gets late to go home late...