Michiru Kazusa

Kazumi is actually the 13th clone of Michiru Kazusa. Michiru became a magical girl the day her grandmother died. She was studying abroad when she learned that her grandmother's condition became critical. While hurrying home, she ran straight into a witch's barrier. Fortunately, she's saved by Mami Tomoe, who destroys the witch with "Tiro Finale". At Michiru's home, a doctor explains that her grandmother only has a few days left unless she's hooked up to a respiratory machine and it's unlikely that she'll wake up. Michiru says that her grandmother would never want to go on life support. Jubey appears on the windowsill, saying that he can grant her wish if she makes a contract and becomes a magical girl. Michiru wishes for her grandmother to return to her normal self as long as she remains alive. Michiru spends the day learning cooking skills and advice from her grandmother. She tells Michiru that people can't fall into dispair as she gives Michiru her earring-bell; the same earring-bell Kazumi has worn throughout the series. Her grandmother passed away the next day. Some time later, she met six girls that were victims of Witch's Kisses and saved them. She convinces them to make a contract with Jubey. Later they became the Pleiades Saints. She saved Yuuri Asuka from a witch and convinced her to become a magical girl to cure Airi. By doing so, Yuuri became a witch some time later. Michiru transformed into a witch while cooking strawberry risotto with the Pleiades. Desperate to revive her, the Pleiades Saints utilized Niko's powers of regeneration and began cloning her from the witch's body. Thirteen of the clones were made; twelve failed clones were hidden inside the Freezer, while the thirteenth - the current Kazumi - has been with the Pleiades Saints. After being exposed to an Evil Nut, Kazumi is beginning to turn back into a witch like the previous attempts. Saki later reveals that her previous twelves clones had lived with Michiru's real memories, but they would eventually become berserk and revert back to witches. The Pleiades' accepted the rejection as "Michiru's will" which led to the decision to give Kazumi fake memories. Source: Puella Magi Wiki