At the beginning of summer, when I heard the sound of cicadas, my sister and Ayame came home from my mother's 17th birthday. I return to my parents' house almost every year because of the existence of my younger sister, Ayame. She is a sweet and longing sister who took care of me in place of my mother who passed away early. Both are married, but I have even more special feelings for her than my own family. And on the night when the trial ended, my father called us mysteriously and admitted that we were not siblings.