They commonly sell such plans even to non-residents, at least at the time of sale, in most (if not all) markets where Apple has its own direct retail sales presence; and I would be surprised if Japan were an exception to that.

I have used my US AppleCare+ plans for US-purchased Apple devices to get service for my Apple devices at Apple retail stores outside of the US; and in some cases the result was that I saved money over doing the same thing at US retail stores ... maybe because of differences in what is covered by the plan from region to region.