That's how it is in a public bathhouse in Japan. The person running the counter is just supposed to not be paying attention to anyone changing regardless of gender.
WE WERE DENIED THE GIFTS OF GOD. Why you this this author? Mari does have taste though.
And it seems like Adashino going to some sketchy places for treatment.
@Esper Well, nowadays they usually have a separator to the locker area where people undress. In really big ones meant for tourists, they would even have a special undressing section with individual booths.