Yunagaya Domain was a minor fudai feudal domain under the Tokugawa shogunate of Edo period Japan. based in southern Mutsu Province in what is now part of modern-day Iwaki, Fukushima. It was ruled for the entirety of its history by the Naitō clan. The domain was initially known as Yumoto Domain

Iwaki is a city located in Fukushima Prefecture, Japan. As of 1 August 2023, Iwaki had a population of 322,019 in 143,500 households, and population density of 261 persons per km². The total area of the city is 1,232.02 square kilometres (475.69 sq mi), making it the largest city in the prefecture and the 10th largest city in Japan (2010) in terms of area. Iwaki is a designated core city, and is also one of the growing number of cities written in hiragana. The present Iwaki City started as the merger of 14 smaller municipalities on October 1, 1966. Every year, Iwaki hosts the Taira Tanabata Festival from 6–8 August.