Karasuma Kumiko wa Miko de Nai

Hero History Apocrypha (勇者史外典) part 3 of 3.

It's the summer of 2015, 300 years before the time of the TV anime "Yuuki Yuuna wa Yuusha de Aru", and "that day" when humanity was destroyed. One of the first Heroes, Takashima Yuuna, has been shrouded in mystery until now, except for the fact that she is from Nara Prefecture. Where did she awaken to her Hero powers, how did she end up in Shikoku, and how did she become a Hero? The story is finally told in the memoirs of Karasuma Kumiko, who is said to be the miko who discovered Takashima Yuuna.