I am Jirobedon writing from Japan. I have some friends who only have vegetables.
Perhaps as you know, Japanese food is tasty, healthy and sightly. I would really like to recommend all travelers our beautiful dishes but it is not easy for vegetarians to find out suitable restaurants in Japan. In my opinion there are mainly two reasons.
Firstly, we do not have lots of information of vegetarianism. Only around 5 percent of Japanese is vegetarian and most of us do not have any chance to think about the restriction of menus. We tend to have various kind of foods and it is so natural to accept omnivorous habits because of a sort of pantheism.
Secondly, this article a little bit relates to the first reason, most Japanese dishes use “dashi (Japanese soup stock made from fish and kelt)” and you do not perceive whether the meal just in front of you contains essence of animals or not. If you would really like to have only vegetables in Japanese restaurant, it might be better for you to ask about “dashi” before trying the dish.
I would like to write the guide for vegetarians both in English and Japanese how to show their requests in Japanese restaurants. I hope it could be useful tool when they trip around our lovely country.