The Mirror of Janus (Janus no Kagami)

Other name: ヤヌスの鏡 / Yanusu No Kagami / Janus’ Mirror

Synopsis:

Ozawa Hiromi, a second-year high school student, lives with her strict grandmother Takako who deprives her of all freedoms. One day, Hiromi faints and wakens to a new personality named Yumi who is the opposite of Hiromi in all ways. Can Hiromi stop Yumi?