I think one of the main impediments to having children is just having space for them. You cannot have a child in a 40m2 apartment, and more is very hard to get in so many places. Certainly not for the people usually inclined to have babies (ie. the poor).
I don’t think that’s strictly true. Flavela housing is also smallish but that doesn’t stop reproduction. It’s more a cultural thing with many other contributing factors, like economic outlook, cost of living, etc.
It's not housing. It's basically lack of time. Japanese are allowed to work almost all of their waking hours. So they do. They pretty much have to because rent is on average always as high as people can afford. Not much time for anything else.
The last time Japan had a population close to replacement rate was 1974, with the population at 109.5m.
Japan will reach that population again in 2046, so maybe we can hope for a recovery by that stage?
Part of the solution certainly needs to be voluntary Euthanasia for the elderly. If you're above 80 and decide you've lived a good enough life, you should be free to go out on your own terms, even without a terminal disease.
I don't know but Tokyo is probably similar.