Saki Asami

Saki is leader of the Pleiades Saints. She has a strict and cold personality, but is very nice and kind to those who she holds dear to. She once had a littler sister, Miyuki, who always loved flowers and dreamed of getting married. However, Saki and Miyuki were in a car accident and Saki was the only survivor. Saki went into depression was about to commit suicide until she was saved by Michiru. To become a Mahou Shoujo, Saki wished that her sister's flower would bloom forever. Saki always loved Michiru. Therefore she could never kill Kazumi, as she holds the same face as her. In the final battle Nico placed a grief seed in her which turned Saki into a witch, in which she destroyed herself. (Source: Puella Magi Wiki)