Ouchi-juku prospered in the Edo Period as an important post station connecting Aizu (parts of Fukushima and Niigata Prefectures) and Nikko in Tochigi Prefecture. Traditionally, the streets were lined with inns and houses providing lodging and meals to transient guests. The town was designated as a Group of Traditional Buildings by the government in the 1980s and has since remained a popular attraction.
Originally developed for the samurai class, kozuyu later spread among the common people and has become a must for festivals, celebrations and momentous occasions in Aizu. In the past, fresh seafood was hard to come by in the landlocked region, so dried scallops and bonito were used to add flavor to the soup, which contains taro potatoes, carrots, shiitake mushrooms and tiny balls of wheat gluten called mamefu.