I think you should be very careful about this. In addition to what
other people have suggested, write down your questions and get written
replies from the government offices involved. I don't know, for
instance, if there are any restrictions on receiving coverage for
pre-existing conditions. And if you do use government insurance you
will be limited to whatever treatments/drugs are covered under the
program, which may not include what you're accustomed to. The Japanese
medical industry may have decided that some other treatment is
preferred, for instance. Also if you work for a company that doesn't
use the government program, there may also be additional restrictions.
So to save yourself some grief later, try to get authoritative answers
before you make any irreversible changes.

M