Tofu is just an ingredient, it doesn’t have to be in a vegan dish

The biggest thing with Japanese cooking is ultimately the heavy use of dashi, which is based on katsuobushi, dried and fermented tuna that has been shaved into flakes. It’s a stock that’s not necessarily in everything but it’s in a lot of stuff

Agedashi tofu is a good example. Delicious and would appear vegan. Tofu, drained, pressed, dusted with potato starch, and fried. Place in a bowl and pour a broth/sauce of dashi, shoyu, mirin, and sugar. Top with grated daikon, ginger, scallions, and shichimi togarashi. There are other ways to make it but that’s a general prep.

The dashi makes it not even vegetarian but at a glance it appears vegan. It’s easily made vegan because you can make a reasonable dashi with dried shiitake in place of katsuobushi. This will not taste the same of course but it will still be good. This is very much not traditional though and is extremely unlikely in Japan

There have been places to get vegan options in cities like Tokyo for awhile though. Despite that Japans definitely one of the more vegan and vegetarian unfriendly places you could travel to. Non vegan restaurants often simply won’t have an option for you and traveling outside of the cities often means no options at all unless you’re good with konbini stuff the whole time. That said Japan is super hospitable; if you explain your diet to wait staff they’ll almost always accommodate in my experience. This of course may require you to have a reasonable command of Japanese, especially if you’re not in a place like Tokyo, and you should be prepared to eat a lot of fairly simple (but still very good) dishes of mixed vegetables in soy sauce and mirin. Also don’t be surprised if they introduce you to natto haha