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.
Despite the fact Japanese are blatantly racist they have a lot of muslim immigrants too. Some Japanese racial genetics calculated that Pakistanis are DNA siblings to a Japanese race and allowed lot of them to move in to revitalize their demographics. I’m not sure it has really contributed to a Japanese gene pool but it has affected a criminal situation for sure.
The problem is, they are poor travelers.
Unlike their Korean counterparts, I feel the Japanese have a superiority complex which rules out any form of real dialogue.
Here in Indonesia, you rarely see the Japanese venture from their own circle, whether it be schools, supermarkets, or territory.
The beauty of the "Korean Revolution" is that they have embraced "multiculturalism" whilst stubbornly sticking to the teachings of their own culture by NOT allowing the government, the media, the UN or even education to dictate to them who or what is Korean.
When I was there they shipped out a lot of Africans when their economy went sour. The Africans were doing jobs that were beneath the average Japanese. They canceled their visas and gave them 90 days to leave the country.