Japanese police are like every other police force in the world and should treat everyone fairly. That said, I think they have a biased opinion favoring other Japanese. If you're not looking for trouble, you should have no problems in Japan. Japanese people, tend to go out of their way to avoid conflict and even when they're drunk, they're more jovial than violent. I'd sometimes walk home from a late night out in Osaka or Tokyo, after the trains had shut down, and never once felt my safety was in jeopardy.