[Nyororin]

I really think that you would have to be forcing yourself in order to not eat any non-Japanese foods while in Japan. I have no idea how long I could go, because at no point in Japan have I ever felt deprived of any food I liked. There are a very small number of things that I liked (or that were "comfort" foods) while in the US that are not available in Japan... But I have gone around 10 years without eating most of them. And if I REALLY wanted them, I could pay for them to be imported.

I think that if you believe you can never eat something again, you will feel much much more deprived than if it`s just a pain to get or expensive. Or if you realize that 95% of things other than ultra-processed-pre-packaged stuff can be easily made at home as Japan has no shortage of ingredients available.

These days the only strange thing I occasionally miss that CANNOT be acquired (in my experience) in Japan is cheapy macaroni and cheese with Lawry`s seasoning salt. It was never a favorite food, never ranked on a list of foods I enjoyed... But for a period of time it was probably the main food I ate. My mother spent all her money on "partying" and didn`t buy food for me and my siblings...Basically leaving us with nothing to eat. Church food pantries would hand out packs of cheapy generic macaroni and cheese boxes to kids who came begging for food.
We had an old deluxe sized package of seasoning salt and a working electric stove...