This is coming from the bottom comments (around #55 to #61 as of this posting) on Debito’s recent entry about expats.
The claim is that there is a form that one must fill out in order to stop the billings. But I think it’s possible for them to stop, simply by sending a letter, explaining that you left Japan. (This is not the dodge where people pretend to “leave” Japan in order to get off the National Health Insurance.)
It sounds to me like some of the posters conflated a form that is used for PR (permanent residents) to discontinue payments while they are not physically present in Japan. I don’t think you have any right to be in either program, though, if you don’t have status of residence.
Some of the comments in response seem to go into that area of snarkiness, where I’m not sure that these people are any more than 50% serious about the question. It’s a good question.
As an aside: When the IBM Japan role (see earlier posts) ended in early 2009, I did re-enroll in the kokumin kenko hoken. Since the payments are based on the prior fiscal year, not only did I have to pay, but the amount was the maximum in the program—because I had a good income. So, yes, I did have to pay those, but I got a tax deduction in 2010 for those amounts. The kokumin nenkin is delayed if you have unemployment, but one is not eligible for the months that you don’t have status of residence. There is also some amount of administrative relief when income is below a certain level.
I don’t think it has to do with whether they choose to bill you or not, or whether they know or not, or whether they get the information on the proper form. They can always find out by calling immigration or going to the ward desk for alien registrations.
[Update: In furtherance of why the comments are a bit of bunk, notice how Kobe City makes no mention of forms on its checklist of "to do" things before leaving Japan.]
[Update #2: You might notice that the various materials the Japan Pension Service is asking as proof of leaving go to the issue of claiming the the Dattai ichi-ji kin (One-time lump sum refund). You are not required to withdraw your pension claim this way, and I generally advise to avoid taking the lump sum, since the annuity is more valuable.]
[Update #3: Here's one that says, when you leave Japan, turn your Blue Book in! Like hell am I going to do that! That's part of the proof I was in to begin with. See? This is why you shouldn't take advice from trolls.]
[Update #4 (5/31/12): More troll commenting, below, that I'm letting through to show that these people just keep it up.
The person alleges to have phone calls around, and claims that if you leave a municipality and turn your card in, the "debt" will just keep growing until you produce pages off your passport. I disagree. Shibuya Ward disagrees, too, at least on what they put in English on their website:
* When a person moves out of Shibuya or leaves Japan, the NHI certificate becomes invalid on the day after the departure date, and must be returned. If the certificate is used after that date any medical fees incurred will have to be repaid in full. The NHI certificate should also be returned upon enrollment in an employees’ health insurance plan, when a person begins to receive public assistance, or if a member dies.
Nothing about special forms or proof. You no longer have your card, you are out.]