I was seduced by the older sister I had always dreamed of as I was about to get married...

Yui-nee is a childhood friend who is about to get married. Her marriage partner is also a brother who lives nearby, where she acted like her real brother. They're supposed to be the two of them, but I couldn't congratulate them from the bottom of my heart...One day, the lady showed me a true face that I had never shown to anyone. Her appearance is incredibly lewd to the usual neat Yui-san... "I'll marry that person, but let's have lots of sex?"