Hmm, the first city we visited was Fukuoka and basically all 7-11s and the other mini-market chains were staffed by foreign workers. Lots of (Asian) foreigners around the central train station as well. We saw the same in other cities as well - Kobe, Kyoto, Osaka.

It's true that once we went into the countryside there were a lot fewer foreign workers, but that is also how it is in western countries.