My beautiful sister and I, who should never be able to touch her, are stepchildren who are not related by blood... On a summer day, when the two of them, who have lost their bondage as siblings, fall in love with forbidden creampie affairs.

At the end of the hot summer, I was heading home to my parents' house for my mother's 17th anniversary. Every year, no matter how busy I was, I used my sister Yuka to go home with a reason. My sister is a woman I admired, having always looked after as a mother since she lost her mother as a child. They are now married, but I have always had more feelings for my sister than my siblings. That night, after the memorial service, our father called us out and confessed that we were not a real sibling...