I worked at a onsen for a month in 2004. I was an intern learning Japanese so they were easy on me, but the ladies working there were doing 6.30am to 9.30pm, every day (including weekends), no pause. The hotel owned the apartments they lived in, and everything in the town was run by onsens, so there was no "job market" really to play. I don't know how much they were paid, but it didn't seem like they were rolling in it. Many of them were complaining about their husbands not working, drinking etc., so I can only imagine that at 9.30pm, they would actually take care of everything in their homes as well. One day, one of them just collapsed, and she was given a day off.
Yet, the workers seemed to accept this as "business as usual" and were generally good-spirited. They were totally screwed over by management, cause the hotel was really expensive, and they knew they were being taken advantage of. But such is the effect of culture on people.
Anyways, all this to say that I think that pretty much every job in Japan would be seen as the darkest shade of black in the West. And I can't imagine how awful the conditions must be for the blacker companies in Japan.