The city of Daisen was established in 2005 from the merger of the city of Omagari, the towns of Kamioka, Kyōwa, Nakasen, Nishisenboku, Ota, and Semboku, and the village of Nangai. Fifteen minutes’ ride in the car from Omagari Station takes you to the ruins of Hotta Fortress, which was set up by Yamato dynasty in the 8th century.