My wife and I have both been vegetarians for the last 30 years. On our recent visit to Tokyo, we were constantly challenged to find food.
There's a dutch person who sells a short guidebook on vegan restaurants in Japan. I don't have his URL handy, but his email address is
. Just ask for his Vegan Guide to Japan, or something like that. It's in English and Japanese, so no problem there. He charges about 20 US dollars for it.
However, I fear that this guide may soon be a bit out of date. One or two of the restaurants listed were long gone. And of course finding any address in Japan can be quite a chore -- Google Maps is your best friend.
Eating vegan in Tokyo means avoiding almost all restaurants (as with everywhere, I suppose). However, if you're lacto-ovo, you can probably get by with Italian (real Italian, not the Japanese version of Italian), Indian (I assume that's what a previous poster meant by "curry"), or even some pastry shops.
If you're someone who must routinely deal with the wretched state of baked goods in the US, you will be amazed at the prevalence of decent pastry in Tokyo. Of course, most Americans have been raised on faux pastry from Dunkin Donuts or the like, so many of us wouldn't know or appreciate the good stuff if we were slapped in the face with it.
In a pinch, you can always rely on grocery stores (not convenience stores). These will always have real (slightly expensive) vegetables and fruits. It's worth a visit even if you're not buying, just to see the different varieties of produce.
One word of caution: the Japanese don't understand the word "vegetarian," but many of them believe they do. It's not that they think fish is a vegetable -- rather, I suspect they probably just can't conceive of someone not eating at least a little seafood here and there.