My mom lets you have sex, your mom lets me have sex. Incestuous mother-son swapping sex - Shinobu Oshima, Yukie Mizukami - DTKM-045

The story of the second mother and son: The adopted brother is staying at his house because his house is being renovated; the son brings his girlfriend home but can't forget his desire for his mother, regardless of how many times his girlfriend and mother have sex. After a neighbor sees this, he discusses with the son whether he wants to exchange mothers for sex...