Big deal. My mother was married to a Japanese for six years. First time I had underage sex, I was 13, with other men (cleverly guided into the situation by an adult) was in the room of a hot spring hotel in Japan with the father of our hosts. He paid two Filipino boys (no offense meant, I love Asian men and am married to one) to service us in our rooms for a start and than took it all the way further for himself. He had called the reception for the service.
Elderly ladies literally pushed the boys into our room. And yes everyone gets washed and cleaned up BEFORE entering any hot spring. And that was in the 70s already.
Beside that being naked in NO big deal in most of Japan. I have sat many times with an entire family and my mother etc in a big bath when I was a teenager. And yes my mother sent me out when by accident I got an erection while stepping into one bath. The same bath were my “instructor” played with me 2m from my mothers spot. Privileged Japanese have big family bath designed in the most elegant ways and it’s an honor to be invited to share.