Au-pair as a form of stay abroad has not yet been able to establish itself properly in Japan. But there are still good opportunities and places. As an au pair in Japan, you need a working holiday visa, which allows you to live and work between 6 and 12 months in a Japanese host family. In everyday life, you work around 6 hours a day in your host family. In your free time, you have the opportunity to take professional language lessons. In return for your work in the family, you get free food and lodging as well as pocket money for leisure and personal needs.
You should know that for au pairs in Japan, in any case, there are no uniform regulations about insurance, working hours, etc... Be sure to settle everything before starting your job in the Japanese host family.