Vegetarianism is not common in the Japanese countryside. Please double-check the Vegetarian Type which the service provider can accommodate to make sure that it meets your needs. Often being able to eat trace amounts of the ubiquitous Katsuo Dashi (fish stock) makes it easier to find options.
NOTE: It is difficult and not culturally sensitive to change meal requests, or make new meal demands, onsite when you arrive at accommodations. Vegetarian types must be confirmed during the reservation process and respected during your visit.