My son started living alone in a one-room apartment in the city.. My parents take a train from the countryside to Tokyo to check on their son.. Seeing my messy 6 tatami room, my kind mother-in-law, Yui, laughed and said, ``Let's clean up a bit,'' and quickly cleaned up the room.. That night, the father has to return home in a hurry, and the mother-in-law ends up staying at her son's apartment.. Seeing his mother-in-law's bulge sleeping peacefully on a six-tatami mat with futons lined up, her son Musco can't stand it anymore and gets an erection...! .