The largest immigrant group in Japan is Chinese (including PRC, Taiwan and Hong Kong); second largest is Koreans. Many of the Korean ethnic minority are descendants of those who immigrated in the first half of the 20th century (when Korea was ruled by Japan), much of whom have never become Japanese citizens (Japanese citizenship is based on descent not birthplace–a very common policy worldwide), although there has also been much more recent immigration from South Korea. Another major immigrant group are Brazilians of Japanese descent.
I've only been to Japan once (on business), but while I was there I was introduced both to Koreans and to Japanese Brazilians; my Brazilian colleague was not expecting conversing in his native tongue to be a feature of that trip.
> the two I’m familiar with, Poland and Hungary, are notoriously anti immigration (at least within the context of the EU).
Poland and Hungary are opposed to accepting large numbers of refugees, especially non-European refugees.
But they aren't opposed to immigration in general. In 2021, legal foreign residents of Poland included [0] over 250,000 Ukrainians (mostly refugees), over 30,000 Belarusians, over 20,000 Germans, over 12,000 Russians; Poland doesn't restrict immigration only to the EU (or Europe), since the fifth highest foreign citizenship in Poland is Vietnam (over 10,000) and the eighth highest is China (over 6,000). Similarly, in 2022 Hungary [1] had over 17,000 legally resident Chinese citizens (third only to Ukraine and Germany; a decline from its 2018 peak when it was almost 20,000) and over 6,000 legally resident Vietnamese citizens (sixth most common foreign citizenship).
Citizens of most OECD countries do not find it difficult to be accepted for immigration by Poland or Hungary; low demand is a bigger limit on their numbers than government policy.
If you want to talk about a country which really is anti-immigrant, Saudi Arabia is a good example – although it has millions of temporary foreign residents, gaining permanent residency was basically impossible prior to 2019; now it is available, but only if you can afford the fee–over US$200,000. Acquiring citizenship is still extremely difficult, up to the selective whims of very senior government officials; the only people who have reasonable odds of being successful in their application are foreign women who marry Saudi men. Becoming a permanent resident or even citizen of Poland or Hungary is vastly easier.
[0] https://en.wikipedia.org/wiki/Demographics_of_Poland#Immigra...
[1] https://en.wikipedia.org/wiki/Demographics_of_Hungary#Foreig...
I don't know where this idea that "Japan has no immigration" comes from – it isn't true.
According to OECD statistics, in 2019 Japan (population 125 million) had net permanent immigration of 137,824 people. Compare that to fellow OECD member Mexico, with almost the same population, which in 2019 only had net permanent immigration of 38,704. [0]
In 2019, Japan's population was 2.2% foreign nationals. [1] While that is at the low end by OECD standards, it is still ahead of Hungary (1.9%), Lithuania (1.7%), Slovakia (1.4%), Turkey (1.1%), Poland (0.6%) and Mexico (0.4%).
According to MIPEX [2], the ease of gaining permanent residence in Japan is on par with the US and New Zealand, modestly easier than France and the UK, significantly easier than Switzerland or Australia. The worst country was Saudi Arabia, with UAE not far behind; equal first in ease were Brazil and Finland, with Sweden, Mexico and Ukraine equal second, and Hungary and South Africa equal third.
[0] https://data.oecd.org/migration/permanent-immigrant-inflows....
[1] https://data.oecd.org/migration/foreign-population.htm
[2] https://www.mipex.eu/permanent-residence