The interesting difference to eg. the Meiji revolution, and what makes this really uncharted territory, is that the extreme aging of Japan makes both democratic and violent upheaval near-impossible. You can't vote out the bastards, because the pensioner vote outweighs the youth, and any violent students/revolutionaries will not be able to get the majority of the population on their side.
As a practical example, my father-in-law was a salaryman with a rock-solid pension and amazing health care (a month in a hospital costs $50, etc). His generation has no incentive to change the system that has worked for them -- even though it imposes an increasingly unsustainable burden on the ever-shrinking working generations paying for it.
If and when it happens, a sharp transition would include seizure of debt assets owned by your father-in-law's generation. Either through default or inflation.
Furthermore I understand, but cannot provide evidence, that 10% of true believers is enough to revolutionize a whole population. Indeed the Meiji succeeded with only around 10% support.
As a practical example, my father-in-law was a salaryman with a rock-solid pension and amazing health care (a month in a hospital costs $50, etc). His generation has no incentive to change the system that has worked for them -- even though it imposes an increasingly unsustainable burden on the ever-shrinking working generations paying for it.