After returning home early from a trip with his father, Yuuji accidentally witnesses his older brother and stepmother Rihō engaged in a secret rendezvous. Though he has secretly harbored feelings for Rihō, seeing them together fills him with intense jealousy. Sensing his emotions, Rihō agrees to sleep with him—just once. But after that single encounter, Yuuji begins pursuing her relentlessly throughout the house, unable to control his desires. Torn between guilt and passion, Yuuji struggles to decide what to do about his forbidden relationship with Rihō.