Most Japan operators hand vegetarian travellers a photocopied note for restaurant staff and hope for the best. Japanese menus rarely have English labelling, dashi (fish stock) hides in things that look completely vegetarian, and "no meat" doesn't automatically mean no fish, no egg, or no root vegetables — all separate concerns for a Jain traveller specifically.
We don't leave that to chance on the day. Meals are planned in advance as part of the itinerary itself, Jain-specific requests included, so eating well in Japan isn't something you're negotiating restaurant by restaurant.