Japan's justice system has it's flaws just like everywhere else, but they absolutely don't sweep crime under the rug.
They're testament to the successes of a homogenous society at the very least.
I don't know if it's due to something genetic, or because of something Japanese people do after they're born.
FWIW, Asian Americans in USA also tend to live longer than other ethic groups.
Now that I think about it, I realise USA might be a good natural setting to study these kinds of differences because there's a lot of people from a lot of places over there, unlike other countries where the population is more homogenous. Or maybe I'm wrong (I'm not from USA, but when I visited there I was astonished by the number of people from all over the world who were there).