Like her friend and apparent mentor Eleanor Ashbury, Dr. Harmony Bannister was once the Slayer's little sister -- but in Harmony's case, the truth about Melody Bannister didn't come out until she was already dead and gone, and the young woman discovered her older sister's secret diary. What she found enraged her: not only had Melody been conscripted to fight a war waged by a bunch of old British men in a stuffy boardroom somewhere far removed from the field of battle, but her personal Watcher, Nigel Hampton Pierce, had apparently seduced her. Though Nigel's academic career was effectively over already, Harmony vowed to make sure he never got a reputable job again if she could help it, and began trying to figure out how she could take down the Watchers Council as well.
In her investigations, she somehow made the acquaintance of Dr. Ashbury, an occult expert who shared her pain and took the young woman under her wing. Her guidance did a great deal to bring Harmony back from the edge and prevent her thirst for vengeance from consuming her; in time, she even managed to coax Harmony back on the path she had always meant to travel, the path that her sister had once encouraged her to follow. The young woman made it through pre-med and medical school, and finally took up her residency at Upton Medical, the one teaching hospital in Shadowgard -- conveniently close to Ashbury, and not-at-all coincidentally, in the very same town where Nigel Hampton Pierce had settled down.
Though Harmony tends to come off as much more sympathetic, kind and warm than her mentor, she's even more militant in her dislike of the Council. The young doctor has never tried to become a Watcher herself and does not trust even this so-called new Council at all. She continues to assist Ashbury out of loyalty, and treats the injuries sustained by local Slayer Taryn Maddock and her friends out of sympathy and respect for their fight, but she may never again entirely trust anyone calling themselves a Watcher.