Most people, when they first arrive, work at a place like Nova, probably the biggest employer of native English teachers in the world. By dint of their overseas recruiting programme, NO-VAcation (as we called it when I worked there) is the first employer for many arriving in Japan. But even this has changed. Recently, after a long struggle with the local General Union, it was forced to provide its full-time teachers with health, pension and unemployment benefits.
http://education.independent.co.uk/careers_advice/article348582.ece