Kore wa Ai de, Koi ja Nai

From Lovesick Alley:

Contrary to her girly appearance, Yaotome Ren is still inexperienced in love because she dreams of having a once-in-a-lifetime romance. Enter Hidaka Yuusei, whose sadistic and strict attitude annoys Ren, and because of that, the two don't get along. What's gonna happen if one day, Ren wakes up from an accident, only to realize that she's now a different person?!