Lol Yeah I've seen how nice they are, idk if you know this channel but I watch this channel called CTFxc and he did some vlogs @ Japan. So I know how they're generally are. They seem pretty nice! Yeah once I make enough money to retire, I first gotta pay off my student loans for uni. & prob. give back to my parents then I'll move out there or visit.
I should note that Tokyo is an exceptional example.
You're less likely to find prejudiced natives there because of the cosmopolitan element; people are more conditioned to mingling with other races. But I should note that even some shops and areas of Tokyo are off-limit to foreigners - I'm no a stranger to the "Japanese people only" sign, although it's far less prominent in Tokyo.
Racism in Japan isn't how you might think though, it's rather soft. Like my first trip to Nagoya, where I experienced some people being avoidant (wouldn't sit next to me on the train, being purposely difficult etc). There was also some bad-ass kid walking with her mother, who pointed to me and said "gaijin" in the street; which promptly led the mother to tell her to be quiet and pulled her away.
The rule of the thumb is just to take it with jest, I found the latter quite funny really.