Lived in Japan for many years, came back to the USA for many of the reasons you touch on. I knew a few foreigners who had non-English-teacher type jobs, but mostly, it was English teacher or English juku owner. The systemic issues, for young Japanese and for foreigners, in Japan really need to be dealt with if they have any hope of slowing their population decline. So, not going to happen.
Japan is never going to have enough immigration to significantly impact the population decline. Even back in the early 2000s, it would have taken millions of immigrants a year. Now, forget about it.
Living in inaka is not bad but not great either, for most people. So, tiny apartments in or near big cities or large houses in the middle of nowhere are pretty much the choices. Jobs in inaka? Fisherman, elderly care, sakaya, maybe some other generic retail for the eldest sons who couldn’t escape. And, of course, government jobs.
Re: media hype, yes there are still young people. But not enough. Societies need 2.1(-ish) children per couple to maintain population equilibrium. Japan, South Korea, Italy, and several other wealthy nations are way below that. Add in the Japanese propensity to live for a long time, and Logan’s Run becomes more and more thinkable each year. When the population pyramid becomes whatever shape parallel lines || are, the economics of a modern, wealthy society break down.
I gave a PD session for Japanese teachers back in like 2004 or so about why learning English would be helpful, because they might end up with a lot of immigrant children in their classes. (Or, I didn’t say, because you could use your English skills to look for jobs outside of Japan.) Of course, immigration barely happened, and many of those teachers are probably close to retirement age by now. So, my bad, I guess. Someone should do that PD today, because the situation is even worse now.
My understanding is that lower fertility follows higher female education for several reasons, including that women in school - and with access to birth control - prefer to wait until finishing school and starting a career before having children. Countries where women have fewer educational and fewer career opportunities, people often start having babies sooner, and more babies overall.
Another oft-mentioned factor is social safety nets such as social security (as much as that can count as a safety net). Areas with no or weak elder support outside of the family tend to have bigger families. Shockingly, this was also the case in the “developed” world back before they developed. Ask older adults in the USA how many brothers and sisters their grandparents had and it is probably a lot more than the next generation had, and the next, etc.
Do colonized people have lower life expectancy or do their children? Or both? Certainly, exploited people may also be living in (and unable to escape from) a society with poor elder care and insufficient safety nets such as social security or other retirement options. Which, of course, makes having lots of kids a totally rational decision. And also limits the ability of many women to participate in the economy outside of the home, which can also slow the development of the country / area’s economy.