My mom lets you do it, your mom lets me do it. (Ouchi Yukari, Shinomiya Chiaki, DTKM-040)

This is the story of two mothers and their sons. 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 seeing this, a neighbor discusses with him whether he wants to exchange mothers for sex...