Nanayo Rangetsu

A violet-haired woman wielding the July 7 Star Rose Quartz shikifu, as well as control of a familiar in the shape of a butterfly. Often wears a cap and has sadistic tendencies. In volume 4, it is revealed that she is Fumiya's sister but he doesn't know anything about Shiki Tsukai, as she always acts to be very sickly when he visit her. Her reason to wipe out humanity is to create a perfect world for her brother. (Wikipedia)