My only suggestion on this subject is that:
If you are a foreigner coming to live and work in Japan and will be enrolling in the national health care system, enroll in it as soon as possible after you arrive. If you are using an international health care provider when you arrive and wish to switch after 3 months or a year, you will be charged for every month since you entered Japan regardless of the fact you did not use the national plan. Doesn't make a lot of sense, but Japanese bureaucracy does not obey logic.
You can find health care providers for foreigners on
Gaijinpot.