Harukanaru Toki no Naka de: Hachiyoushou

On the first day of a new school term, high school student Akane Motomiya, her classmate Tenma Morimura, and their younger friend Shimon Nagareyama are pulled into an old well and transported to Kyo — a parallel world resembling Heian-period Kyoto. The young scion of the Star Clan, Fujihime, explains what has happened: Akane is the Ryujin no Miko, destined to protect Kyo from the Oni Clan. Eight guardian warriors called the Hachiya will stand beside her — and Tenma and Shimon are two of them. Akane is bewildered by all of it. She grows into her role over time.