Bandai-san might be male or female, but you don't have to worry about it, since
he or she is not interested in what people are doing in the changing room. They
are just doing their jobs as a owner of the "Sentou".
You can enjoy "sentou" at a resonable price. It usually costs about
400 to 600 yen at the most, so you should have small change which will come in
handy whenever you go to "sentou".
Never use a 10,000 yen note. The person sitting at the "Bandai" might
frowns at you if you do so.