[bELyVIS]

A Japanese couple adopts a African (black, can be from any country but trying to be politically correct) baby and you get a black Japanese.

A black (again from any country) couple adopts a Japanese baby and you get an child who looks like a Japanese, but takes after the parent's home culture.

Point being is what most here have been saying, the baby will take on the culture of the parents. Even if the OP raises the child in Japan, the child will never truly be Japanese. This child is likely to be shunned there too because it won't fit in completely.
None of this matters because if Japan won't let me and my Japanese wife adopt a baby there, you don't have a chance either.
I have to agree with Ronin4hire (has Hell froze over?), you need counseling before you do any adopting.