If you're a strict vegetarian or vegan, go about your day in Japan with an abundance of caution. Few places have 100% vegetarian items (outside of boring pasta dishes or margarita pizza), and even fewer can be classified as vegan.

Sauces, dressings, oils...all sorts of things are fish or meat based in some way.

Without being overly negative, the truth is Japan is probably the worst place in Asia to be a vegetarian, though Korea is a close second. (The reason Korea isn't first is because of the large number of international restaurants, at least in Seoul.) Japanese cuisine is not centered around fruits and vegetables, and the number of international eating options is limited.

If you want to visit a veggie paradise, Taiwan stands head and shoulders above most countries in the world. Taipei has a slew of new, world-class buffets that are simply amazing.

Indian food is always a reliable option in Japan, and there's even a high-end, vegetarian-only Indian restaurant in Ogikubo, Tokyo.

The situation is improving. Salad and other veggie options are growing at izakayas like Watami and even noodle chains like Hanamaru. But you need to be vigilant and make sure they don't add ham, bacon, chicken, etc. And once again, there's no certainty that even the soy sauce will be veggie.

If you are strict, one's best bet as a visitor is using websites like Happy Cow that point out veggie-only restaurants:

http://www.happycow.net/

Compared to other places, veggie consciousness is growing at a plodding rate in Japan. But there are new restaurants opening regularly, and the situation is much, much better than 10 years ago.