Japan is the former and Singapore is the latter. Both end up in good places to live, but one has to have the full discussion about the reasons and causes for each.

Also I’m not convinced that executing people for non-violent crimes is a good tradeoff in the first place.

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