Japan is overcrowded. This might not be a bad thing. They already have a big population outside of Japan. The Tokyo-Yokohama area is huge. Nothing but wall to wall apartments. This is about the only area in Japan which is not mountanious, the Kanto Plain.
The solution to the population problem in Japan will be robots.
To maintain stability, the rate of robot introduction must match or slightly exceed the population decline.
The only reason a population stabilization or decline is viewed as a “disaster” is because it means the Ponzi Scheme of the Welfare State that most “Western” countries (including Japan) have been saddled with collapses unless there is a continuous supply of young workers to prop it up. In the past, countries have gone through periods of population stabilization or moderate decline and it has not been an issue.
But, through it all, Japan will remain Japan.
They have not, and will not, allow vast numbers of immigrants to enter and take control of their country.
GOP elites and Dems try to convince us that 20 million unskilled Mexicans will make us a more fiscally secure country as they tap into SS, Medicaid, Medicare, etc having paid little into them.
One more example of politicians wanting reelection over doing what is best for the USA.
The fear of the individual for him/herself will always override the fear a person has for their nation, culture or society. That is why the Democrats win.
Japanese history shows that they are unlikely to allow a lot of immigrants into their country. I would look for them to ship more of their population out to other countries in a sort of stealth imperialism.