Nothing is more important in Japanese cooking than dashi, the fundamental cooking stock that underpins every aspect of the cuisine. There are many ingredients that can deliver a boost of umami savor, both natural (konbu seaweed or shiitake mushrooms) and artificial (various powders out of jars or sachets). But nothing compares to the richness of dashi made with traditional katsuobushi (bonito flakes).
If tasting is believing, then the place to do that is at the Nihonbashi Dashi Bar. This small self-service counter on the ground floor of the Coredo Muromachi building (right across the street from the main Mitsukoshi Department Store) offers two kinds of dashi — one of pure katsuobushi, the other blended with konbu dashi — served steaming-hot in simple paper cups.
Umami has no flavor in itself, so on their own these are pretty tasteless. But add a little soy sauce or salt (provided at the small tables to the side) and they make a tasty, affordable (¥100) drink that's most revivifying on a chilly winter day.