Heian Igaku Shoujo Ibun

Hina, a high school girl who wants to become a doctor, travels back in time to the Heian period during a school excursion! There, she is asked to take the place of Minamoto no Yoshitsune. Her only emotional support is Taira no Koremori, a member of the Taira clan, which is hostile to the Minamoto clan!

(Source: Kadokawa, translated)