swapping, exchange mother and child mating

This is an incestuous drama presented by a mature woman, old-fashioned Ruby. After his father's death ten years ago, he has been in a relationship with his mother Miju and her close relatives since 7 years ago. As expected, after seven years, the prohibition relationship will also become manneri. One day, he tells Hiroaki, his cousin in the same situation, that he has a relationship with his mother, and he finds out that it was the same incest relationship. These two people think of ingenuity, 'Let's exchange your mother.'