From Transcendence
Azusa, a normal high school girl, fell down the stairs while visiting her grandmother in the hospital two months ago. When she awoke, she was surrounded by people speaking of "The Priestess of the Dragon God," "The Imperial Capital," and "The Taisho (Era)."
The legend starts again with this work, commemorating the 15th anniversary of the Haruka series!

From Viz:
Akane is your typical teenage girl...until she swallows the Dragon Jewels, which transport her to the Heian period of ancient Japan! There in the capital city, Akane learns that she has been foreordained to lead the people as the Priestess of the Dragon God!