Has that shortage actually been driving up salaries? From what I know, Japan has the worst "SWE Salary:Cost of living" ratio anywhere in the developed world.
Citation needed. My salary here is great by local standards. If you're comparing to the US, don't. Salaries in the US for SWE are much higher than anywhere else.
I was intentional when I said "the developed world", so including Western-Europe, South Korea and so on, not just the US. The fact you're on HN speaking perfect English already means you're likely to be very much above the median, salary-wise.