Ria Kashii is the stepmother since the older son's mother passed away, then his father, unable to bear it because he was still in his prime, took a young, beautiful wife. After living together and wanting his son to call his stepmother his mother and wanting to be treated as a son, he told his son. Then everything started when the stepmother sexually assaulted her husband's son and the son became horny. In the end, the son raped his mother and began an incestuous affair.