The nun (including before she was a nun) is one of my 5 very favorite characters, and was long before she was a nun. She's also and interesting twist on her trope long before that.

(I have my one ultimate favorite, Miria, but 2-5 tends to remain the same four, but the order changes.)

ETA: I should also warn that Claymore's mangaka doesn't care if a person is a blatant redshirt or a fan favorite. If s/he(no idea) decides it's time for someone to die, everyone is fair game, and seeming redshirts don't die and become well developed characters.