I'm looking for restaurants that are single diner friendly at lunch time.
I'd be more concerned about being an 'anglo', anglo, than dining alone -at lunch or dinner, singletons are always accommodated in this town.
As everyone said, Most restaurants are single diner friendly ( not all). Red Farm for one didn't like seating singles, Nakazawa won't take singles, so there are exceptions.
However, most sushi bars in the city are perfect for single dining, Telepan Local is a good single dining spot for small dishes, Casa Mono for tapas, Yokocho, Terroir Wine Bar ( good meatball sandwich), Osteria Morini at the bar, Kyo Ya at chef counter, Brushstroke, etc etc etc