About the one lump sum payment. You have to go to the Pension Service dept and get the paper work. I think it is in both Japanese and English. You do not get the payment here in Japan. You go back to your home country, set up a bank account, fill out the Pension Service papers and then mail them back to Japan. You can expect about 3 to 4 months before you'll get a wire transfer of funds to your account. Ex. If you paid into the account for about 15 years, you might expect to get around \200000 or a bit more. But it worth the time and effort to go to the city and get the paper work. Not sure if they can give you exactly what you'll receive but if I 'm correct, a fairly close estimate.
I went through this process a few years ago, but I ended up staying in Japan. So the above comment should be fairly accurate and useful info for you. But just go to the Dept that handles this and you'll get what you need. Expect to be there for maybe over 45 minutes. Well, at least in a smaller city anyway.
