Sunlight streamed into the bedroom as I woke up with a hangover and realized a woman's hand was touching my body. Assuming it was my wife, I followed the arm and pulled back the covers—only to find Yui, my wife's adult younger sister, sleeping beside me stark naked! She had moved in the day before while looking for a job. I somehow got through the moment without my wife finding out, but from then on Yui began waiting until her sister wasn't looking to tease and seduce me...