Puella Magi Kazumi Magica, Vol. 1: The Innocent Malice — Masaki Hiramatsu

Kidnapped and stuffed into a trunk by an unknown assailant, teenager
Kazumi bursts forth from the confines of the case to discover that she
has been stripped not only of her clothes, but also of the memories of
her life before the kidnapping. When she is recovered by a pair of
schoolgirls, she doesn't recognize them as her best friends and
roommates, Umika and Kaoru. As Kazumi tries to settle back into her
normal life, she quickly realizes that her former "normal" was anything
but!