In Meiji-era Japan, the elite Yamainu unit was assembled to hunt Orochi, a giant snake spirit that resurfaces every three hundred years, and it now finds itself tangled up with a secret government program experimenting on people with Orochi cells. When brothers Soramaru and Chuutarou Kumou cross paths with escapees from those experiments, they have to choose between the Yamainu's captain, Sousei Abeno, and the fugitives, among them a criminal doctor and a test subject carrying Orochi's power. This spin-off from Donten ni Warau was later adapted into a trilogy of Wit Studio films.