Most likely, kelangan ng
1.) statement or passbook of your bank acct (show a substatntial amount there)
2.) either invitation letter of sponsor from Japan or letter from travel agency certifying your itinerary (includes round-trip ticket + hotel stays,etc) in Japan.
3.) Certification of Employment if employed.
just like US visa, aside from bank account which needs to be running, if there are cars, lot under your name show them the papers as well, even if you have large amount of money yet they are on a trust or TD they dont honor it much.