Manga where the female protagonist has amnesia
I believe it is called Otome x Ranbu




  She is your stereotypical airhead school girl, with one exception, she
  has amnesia. She recently transferred into a new school where things
  work different, mainly magic. She is Mochiduki Tsubomi, and she
  doesn’t remember anything before she transferred. Enter yet another
  transfer student – the beautiful yet arrogant bishojo, Izayoi Yukiji.
  She’s after Tsubomi, but why? What does Yukiji want? What mystery does
  Tsubomi hold?