Ive worried about the same thing before with Japan. I am not black (native american, white, japanese) but I look it so it was something I thought about. From what I have heard there are no issues with black men and the Japanese. However I have heard of a few problems with black women and the Japanese. I was reading a few hundred post on another forum site. And several women who were black and went to japan had random people coming up to them one of them was a salary worker who said "yo yo yo whats up my nigga" but that was the only issue she had whlie she was there. Another person said that many peopel told her she had large breast. Another woman said that she was treated like a celebrity the whole time she was in Japan. The guys however had little to no issues. Just got stares but thats usual for anyone in Japan thats not Japanese is it not?
I also remember reading a few comments that said. Japan is probably the best place for black people. Especially if they are from America, since Japan doesn't have many racial issues as the states. Just gaijin ones, but from what ive heard blending in and learning the language is the best thing, and you shouldn't be treated drastically different.
I say go for it
I will be going next year.