The Priestess of Bal Masqué, and their leader for the first two seasons. Hecate is a blue-haired girl who looks about twelve, but is much, much older (she has a reincarnation cycle). Quiet and nearly emotionless, she lives only to carry out the will of Bal Masqué's god, the Sairei no Hebi.
Hecate is Shana's opposite number in more ways than one. Not only are they contracted to the ultimate good and evil entities in the series, they both have their emotional sides triggered by Sakai Yuuji (in Hecate's case, this is via her human duplicate, Konoe Fumina), and they're the two characters who get "chibified" in the DVD extras.
Named after a Greek goddess, with whom she shares some traits.
