The anime adapts Takashi Noguchi’s manga, which itself is based on Baku Yumemakura’s supernatural romance novel. The story follows Minamoto no Yoshitsune, known as Kurou, who retreats into the mountains after being defeated by his brother, Minamoto no Yoritomo, Japan’s first shogun. While history records that Kurou committed suicide, he instead encounters a mysterious, beautiful woman named Kuromitsu in a mountain hermitage. Over time, Kurou falls in love with her, only to discover that she harbors a dark secret. He learns that he is immortal, living for a thousand years as Japan transforms into a future society.