Being a management consultant, I frequently take clients for lunch. As a vegan in Tokyo I have a lot of trouble with this. Really not easy, and the Marunouchi area is one of the hardest areas in Tokyo to square this circle in. My only option so far has been the Palace Hotel's restaurant "Wadakura" where I can get vegan tempura (really outstanding, btw) if I call ahead. Well, this place here - "en" - serves a "vegetarian" lunch that hits the spot. Given the price, one might expect this anyway, but you never know until you try. This is an upscale restaurant with an elegant, intimate atmosphere, spacious interior, well-spaced tables, comfortable seating and impeccable service. They clearly and blatantly target the well-to-do, health-obsessed housewife crowd that have not a worry in the world other than spending money. They make up 75% of the patrons here at lunch time and the menu accordingly offers a vegetarian lunch at 3,400 yen (first option on the menu) and a "health" lunch at 3,800 for those who can't do without animal corpse parts. More expensive options available. The vegetarian lunch is really a vegan lunch and it was outstanding. Consists of six or seven courses, each one of them worth pausing for and appreciating. The "carrot pie" appetizer was sublime, the mabo-dofu one of the best I've ever had (they used fake meat that was indistinguishable from the animal flesh variety), the sweet tofu with sweet bean dessert a becoming finale. Highly recommend this place. Just one thing: you need at least 90 minutes to make it through all seven dishes so this may not work for everyone.
Cons: Not for budget travellers