The boys in the movie are really happy to have their very promiscuous cousins. The cousins not only help them clean up the room, organize things neatly, but also are a wonderful sexual tool if used properly. Of course, for boys addicted to sex like them, they cannot be ignored. The cousins constantly reveal sensitive areas such as firm buttocks, huge breasts that the older brother accidentally sees while the room only has two people. So it's no wonder that incestuous relationships often occur in Japan, which is very clear in the 3 parts of the movie.