Japan has always been a strange country with unique customs, and this movie is a testament to one of those customs that perhaps not many people know about. That is the custom of face-palming and licking women's private areas every time they meet or hold a party together.
It sounds very unreasonable, but Tanaka's wife went from being a person who felt disgusted about She has adapted to that and found it extremely interesting after spending some time with her husband's family and learning about this traditional practice. The son licking the mother, the father licking the daughter, the brother licking the younger sister is something that happens every day in this sexually immoral family.
This is certainly a family that puts women first and they Consider actions like the above as the best expression of that. Another special thing is that every time the family has a new member, there will be an introduction ceremony, meaning that person will have to strip naked and let everyone in the family of the opposite sex participate in the relationship. Group sex includes father, older brother, younger brother or husband - that is Tanaka's case.
