have you been there before? i'd highly suggest at least visiting before making such a huge jump.
as for youre questions, i was just copying and pasting the exceptions to the rule from that website (which is why it says refugees, obviously this isn't your case) ...to get an exception is very difficult, look at that first website i posted (
Permission for Permanent Residence ) and see what types of people they accept. Honestly I canot comment because I have no experience. However I do know a few things, if you want to work in the medical field in Japan you have to pass JLPT level 1 (japanese proficiency test) ...and to live in japan working in the medical field you'd have to have your employer sponsor your working visa. Thennnnnnnnnn you can talk about making significant contributions toward society.
Basically you're biting off more than you can chew right now. Concentrate on getting there first as a worker (not at all an easy task), see how you like it and go from there.
Hope this helps.