JUL-587 My beautiful sister, who I would never mess with, and I are stepchildren who are not related by blood... - On a summer day, the two lose the bond of being siblings and indulge in a forbidden affair. - Riho Fujimori

On a summer day when the sound of cicadas was loud, I was returning to my parents' house for the first time in a while to mark the 17th anniversary of my mother's death. - My older sister Riho was a big reason why I made sure to come back every year. - She was the older sister I admired, who took care of me all the time in place of my mother, who passed away at an early age. - Now that I'm an adult, my sister and I are both married, but I still have special feelings for her that are different from my siblings. - Then, on the night after the memorial service, my father called me to talk, and there he confessed to me that he and my older sister Riho were not really siblings...