Yushiro and Miharu follow the long-lost Path of the Kai to the threshold of Kyoto, home to the lost secrets of Yushiro and Miharu's past. Upon touching the threshold, the two young kais are given a glimpse of Japan in the Heian period, around 1,000 A.D.. The story tells of a disagreement in the Watanabe clan, the last protectors of the secret of Gasaraki. This disagreement leads to the accession of warlord Tsuna Watanabe who intends to use his clan's kai, Yushiro and Miharu, to reassert its power in the face of centralizing imperial power.