The Israeli jewelry sellers worked for yakuza? They were in Sasebo too.
They are everywhere, they go on a short trip to Laos or Thailand, and then reapply for a 6-month visa to Japan again. The Yakuza will pay for the trip and also for the immigration free.
Most jewlery sellers are Israeli or Arab, but there are quite a few Western Europeans and Africans mixed in. All the others have degrees and teach English or translate.