Tough question. But for me, it's the Ministry of Health, Labor and Welfare estimate that approximately 250,000 people may have lost an average of 380,000 Yen each due to the five-year statute of limitations on pension claims. That's a good number of zeroes, but it's a little over 3,000 US Dollars (the rest of the world please do your own math), enough to allow an elderly couple live comfortably, provided they've already paid down their mortgage and don't face catastrophic medical costs (and their kids stay in work, and out of jail), for a month. They could probably stretch it out to two, or even three, provided they didn't go out much.
True, MHLW may have an incentive to underestimate. But it doesn't look like a very generous deal to begin with. What's it like for you back home?