The reason why the mother-in-law who was living together left the house was, surprisingly, the "father-in-law's impotence"... The two of them were trying to comfort the grieving father-in-law and doing exercises to promote erection, but the father-in-law became desperate because it didn't work. When Serina tried inguinal massage, the father-in-law's dick, which hadn't gotten hard no matter what, gradually grew bigger and had a full erection for the first time in 6 years! "This may be the last erection of my life... Please remind me of the joy of being a man just once!" To the father-in-law's desperate plea, risking his life, Serina, feeling sorry for him, allowed sex in secret from her husband...