Regarding your specific query about a 12-year-old girl and a pee bath, I couldn't find any information that suggests this is a common or widely practiced cultural tradition in Japan or elsewhere. It's possible that you might have come across a misunderstanding or a very isolated incident.
to urinate in public baths, pools, or other shared water facilities [40, 44]. Forest Bathing ( Shinrin-yoku japan 12 yo girl pee bath
