If you stay in Japan long enough, there will come a time, equal to that of the Super Lotto, called "ongaeshi," when you have to pay back people who have helped you along your rocky limestone road to a comfortable life in Japan. I'm pretty sure that's why Japanese people always ask how long you have been in Japan -- so they know if it's acceptable yet to cash in on ongaeshi. I'm not in any way suggesting ongaeshi is evil; it's just Japanese.
Ongaeshi comes in various forms, the ultimate being a request from someone like your landlord or the parents of longtime private students for a home stay in your home country. At this point, forget about the favors your landlord has done for you or all the income you made off those private lessons, because you are now going to pay every bit of it back in the form of food, entertainment and gifts during their home stay -- which, by the way, they have been waiting years for.
You see, every Japanese person has a secret hope when they meet a "gaijin" that that person will take them for a home stay. "Home stay" is a magic word in Japan because is believed that home stays bring fluency in English, a language that, as you know, is learned through osmosis in all countries except Japan. Every time a foreigner moves back home from Japan, he or she is dashing the hopes of someone, somewhere who now has to mentally cancel their plane reservations and planned English fluency.