Japan have local board, you can ask them about how to buy bitcoin and will find some people know about that.
It's no use, the board consists of posts that are mostly marketing. It's an active board because there are posts coming in but having conversation there, I don't think that he can get some help there from native japanese or someone who's living on that country.
Better to look for the other options that suits him.
@OP have you found a solution?