Karakuni Jinja is an old Shinto shrine, categorized as shikinaisha, a highly-valued shrine listed in Engishiki*. Its construction dates back about 1,500 years ago, as mentioned in Nihon-shoki, the second oldest book of Japanese history. Karakuni Jinja was originally dedicated to Nigihayahi no Mikoto, who is believed to be the founding father of the Mononobe clan. In the Muromachi period (late 14th century), the shrine included Amano Koyane no Mikoto and was moved to the current location. In the late Meiji period (20th century), the shrine merged with the local Nagano Shrine; now it also houses Susanoo no Mikoto, to whom Nagano Shrine had been dedicated.
*Engishiki: a book of Japanese law and customs compiled in the middle Heian period (early 10th century).
Domyoji Tenmangu was originally called Haji Jinja, a shrine dedicated to the patron god of the Haji family. But after the nation-wide deification of Sugawara no Michizane (a member of the Haji family), the shrine also started worshipping Michizane and was renamed Domyoji Tenmangu. As a tenmangu*, Domyoji Tenmangu is thought to be as old as the famous Kitano Tenmangu (Kyoto) and Dazaifu Tenmangu (Fukuoka), both of which were built about 1,000 years ago, in the middle Heian period. Among the more than 12,000 tenmangu in Japan, only Domyoji Tenmangu preserves Michizane’s genuine relics, which is solid evidence of the historical relation between Michizane and the shrine. Domyoji Tenmangu houses a number of treasures registered as Important Cultural Assets and National Treasures, including the Michizane relics.
*Tenmangu is a Shinto shrine which worships Sugawara no Michizane as Tenjin.