This festival is held every year during summer (dates may vary because of the current coronavirus situation) by the Shonai Shrine.
During the festival, visitors can attend several historical reenactments and religious ceremonies in the glory of the Shonai Clan.

About the Shonai Clan:

The Shonai Shrine enshrines the souls of the Sakai Family, lords of the Shonai region, from 1622 to 1868. The Sakai Family, head of the Shonai Clan, was reputed for its high education standards and its military excellence. During the Boshin War (1868), the Shonai Clan, who had sworn allegiance to the Tokugawa shogunate, fiercely fought to the end without losing even one battle. The Shonai Clan eventually surrendered when all its allies (especially the Aizu clan) were defeated. After the victory of the New Government of Meiji, the Shogunate system was abolished, and all local lords lost their titles. As a result, the Shonai Clan's castle: the Tsurugaoka-jô 鶴ヶ丘城 was destroyed in 1871. Instead, the Shonai Shrine (shonai-jinja 荘内神社) was built upon its foundations in 1877 to commemorate the Sakai family and the Shonai Clan.