At the beginning of the summer when I heard the sound of cicadas, my sister Ayame and I returned home on the 17th anniversary of my mother. I returned to my parents' house almost every year because of the existence of my sister, Ayame. She is a kind and longing sister who took care of me in place of her mother who died early. Both are married, but I still have a special feeling for her sister more than a family. And on the night when the litigation was over, we were called by my father with a mysterious look and confessed that we were not real siblings ...