ksandness

The first thing I would want to know is how vital this is for you. Are you gluten-free because you're a true celiac or are you able to tolerate small amounts? I assume your avoidance of dairy and soy is due to allergies. How severe are these allergies? Are you lactose intolerant, and therefore able to tolerate fermented dairy products (I have a niece who can tolerate cheese and yogurt, for example), or will any form of dairy be dangerous to you? This will determine how flexible you can be, and sometimes you have no choice but to be flexible unless eating or drinking something would cause severe illness or would be life threatening. (I used to know someone who went into anaphylactic shock if he ingested the least bit of egg.)

Your main challenge will be foods that come already prepared with soy sauce, which is a lot of them. Most sushi should be OK, except for eel, which is made with soy sauce. Miso soup is made by dissolving miso paste in fish broth, so that's a problem, too. In a pinch, you can find Western-style restaurants all over Japan these days, except in very small towns.

Here, at least, is some information on avoiding gluten:

https://theculturetrip.com/asia/japa...ting-in-japan/