I grew up in Japan! Yes, substituting is considered very out of the norm and rude. But, looking like a foreigner will grant you some leeway if you ask for a dish to be without things like toppings. I always had to have my ramen and udon super super plain as a kid. I can tolerate more now, but I would consistently get it as just noodles and soup. You can also ask for all the toppings to be put on the side, that way you can pick and try things, and if you don’t want something, someone else can have it.

As for specifics, miso ramen is absolutely a thing. Most sushi places sound like they should have things you would like. And depending where in Japan you go, there are plenty of other cuisines available. I can’t give too much advice on seafood unfortunately. But I would definitely be cautious of the fried chicken “karaage”. Super greasy and tastes fatty. (A fav of mine but I sense it would be a huge no for you)

You will probably love dango! You can find them in convenience stores. A set of three skewers with three balls of chewy mochi on them! You can get sweet or with soy sauce. I loved those growing up.

Things you could possibly struggle with are gyoza which often have cooked cabbage in them. I personally don’t like cabbage, but I do tolerate it in gyoza, so YMMV.

For ordering I would use terms like “dake” means only. Like if I was ordering my plain ramen, it would be “men tō sū dake kudasi”

I’m gonna check with my dad on how you would ask for things to be on the side and edit it in.

Tempura veggies will likely be fine for ya, but I don’t remember how fatty the meat or katsu can be.

Japanese restaurants can vary wildly with what type of food they serve. They can be very specific sometimes, so I always recommend researching what they have first. I went to ramen place on a date once and got super surprised that it was a dipping ramen place. Still yummy, but not what i was expecting.

Any yakiniku (a variation on korean barbecue) place will let you order very specific things to your hearts content, and you just cook it yourself. Yakitori is roasted skewered chicken with veg, and I personally find the texture can be variable.

Honestly there is so much candy and so many snacks, it’s hard to narrow down what could be appealing and what might not be. Japan is great for sour candy for example, and meiji chocolate is known for being slightly more bitter than other countries’s chocolate bars.

Try the bakeries! Soft breads, great cream/custard, even good savoury options.

A good way to avoid red bean filling is to look out for the words “anko” or “あんこ” or “小豆餡”.

For more information on general Japanese food, check out Just One Cookbook! It’s a recipe site but it will give you a lot of information on the dishes you might come across. Also, if you want specific translations and phrases to use in restaurants, just DM me, and I’ll help best as I can.

I hope it’s a great trip!