In Tokyo, there was once a youkai-priestess named Yurine who served as the Karas during the Edo period. However, when Ekou turned away from the "shadow path," Yurine had to choose new Karas. Since then, all subsequent Karas have failed before Ekou. Currently, Otoha is Tokyo's last hope. It has been discovered that Yurine holds the secret to a dark force which empowers Ekou, but its specific nature remains unknown.