This is the result of demographic crash and stagnation more than anything else...
You mean interest rates don't necessarily control inflation?
Japan is the worlds first steady state economy and got that way due to a sudden stagnation in trade and then demographic crash over a generation.
They've tried just about anything (except unrestrained foreign immigration or forced breeding) to jump start the economy but nothing has worked.
Inflation is effectively zero...
They haven't tried just about anything. They haven't tried printing enough money.
As a counterfactual: if you can print arbitrary amounts of money without raising inflation, you can just gradually buy up all the assets in the world with newly printed money. As far as I can tell, the Japanese central bank does not own the US stock market or all the gold in the world or all bitcoin etc, yet, so they haven't printed enough money.
Btw, what makes you think Japan is a 'steady state economy'? https://fred.stlouisfed.org/series/NYGDPPCAPKDJPN says their real GDP per capita grew fairly steadily over the years. It's just the price level that has been relatively steady, but if that's your yardstick, than just about any economy that used to be on a gold standard would also fit that idiosyncratic definition.
Exactly, but read many macro textbooks and they will tell you that interest rates control inflation. You've eloquently described a counter example and made the point I was trying to make.