They have the Ainu, the Koreans who came over ages ago to do leather work, and who lived in poverty because of the low esteem in which working with dead animals is held in Buddhist culture (From Tokyo to Jerusalem, by Professor Abraham Kotsuchi, speaks of them), and of course the gaijin who are in Japan on business. Muslims, they keep under tight reign, and don’t tolerate any BS.
Any group, even just two people, are going to have problems. When I was a kid there were two different churches near my home who basically had a civil war and broke into two or more churches each. As far as I could tell, they were all white and the same religion. What the heck happened. But with all the arguments and the breakup, nobody to my knowledge got violent.
It’s when you have people who are fundamentally different, who see the world through a different cultural filter where you end up with violence. I asked my Muslim employee why he planned to have fifteen children. Without hesitation he answered, “We need soldiers for the Jihad.” He was a laughing, good natured guy but in a fit an anger and frustration he once told me, “When we take over, you won’t like it. You will pay me taxes.”