The onsen is a place as relaxed as it is mysterious because it can hide reality with water vapor. In fact a very famous film by Studio Ghibli “Spirited Away” deals with a dark subject, it’s prostitution.
I show you the basis of my opinion. See next Link.
First on that page there is a picture that says “回春 Kaishun”, that means prostitution in Japanese.
Second, the women are dressed in only one Kimono. That kind of Kimono is like pajamas in our traditional culture, so they work in the onsen to clean the clients’ bodies with the pajamas. It is very rare.
It is the kimono for the normal woman. She wears two kimonos.
Thirdly, women wear a lot of makeup and are sexy, but if they work to clean something in the bathroom it is too much.
From a very important scene in that movie that Yubaba stole the name of Chihiro and gave a new “Sen” we can know that Yubaba’s hotel is a whorehouse, because Japanese prostitutes have a different name from the real thing to hide their privacy. Well, Chihiro became “Sen” because of a new person who is dedicated to a night job.
For this purpose, in Japanese prostitution is called “売春 Baisyun”, which means spring sale = young time, and this work has been related to Onsen from many years ago. The culture of traveling around Onsen had been around for 1000 years, and at that time there was a job to clean the body of the clients or to give massage. The women who do this work are called “湯女 yuna = the woman of hot water”. Yuna was originally very healthy, but when the many hotels were built in Onsen, the competition intensified and some Yunas started to make the massage special.
The culture of Yuna still continues in modern times, as there is a job called “Super Companion” like Yuna. In this point of view our culture is like the ancient times.
A registration page for the Super Companion member. It is very easy.
However, the government always hates the depraved culture. It made the ban many times to improve the society, but always the culture of Yuna was reborn because people had demand.
Ghibli’s films seem like works for children, but in reality they are for adults. So I have a doubt, is Kaonasi the symbol of the people who want to buy a girl?