$4K a month, not that bad, although you would pay a fraction of that in Thailand, but of︀ course Thailand is not Japan.
No foreign assets reporting for 5 years, that's nice, 5︁ years is a good amount of time, maybe you won't end up being there that︂ long, again in Thailand you don't have to pay foreign earned income at all, plenty︃ of people moving there just for that reason, and the dating of course. And if︄ you live in Japan and you generate dividends from investments in the US, the withholding︅ rate is 10% as opposed to 15% if you live in Thailand (Japan has a︆ great double tax treaty with the US.)
I spend most of my time in Mexico,︇ cheap, great weather, really nice people, also 10% withholding on dividends, but maybe one day︈ I'll go to Thailand (Chiang Mai.)