That's simply not an option for a country with as big a welfare state as Japan's, unless of course they take the Soylent Green approach, which would seem to be at odds with the cultural respect for the elderly, ancestors, etc. (maybe that's changing). Add the government essentially misappropriating the people's wealth to fund decades of extreme fiscal deficits, to the point of 214% of GDP per the CIA and 238% per the IMF (per Wikipedia https://en.wikipedia.org/wiki/List_of_countries_by_public_de...) ... as more and more people retire, the money they thought they had in their e.g. Japan Post Bank, they're not going to be able to withdraw it, at least in vaguely similar economic terms.
I don't know what the hell they can do, that doesn't involve serious inhuman stuff.