TOFU is the way to go!
As a person who hardly eats any meat, I always look for restaurants with meals for vegetarians. Some of my favorite restaurants are tofu-specific restaurants. Tofu is an excellent source of protein for vegetarians. My favorite restaurant is "Ume-no-hana" in Sky Building in Yokohama Station. I love how the chefs are creative in incorporating tofu in every dish.
It is best to go to this restaurant for lunch, because it can get slightly expensive at night. The food will come out in small dishes, so remember to enjoy each dish to the fullest! The food ranges from chawamushi to fried tofu to yuba to yudofu. These are all tofu dishes with a slight twist. You'll enjoy every dish because it's unique, healthful and delicious!
The service is also excellent. You'll want to come back to Ume-no-hana for more!
Here is the list of stores in Japan: http://www.umenohana.co.jp/n_english/shoplist01.html#5