Kanon Miyamori

Kanon is a sky dweller who, after doubting her relationship with her then would-be boyfriend Kojima, throws her ring -- a gift from him -- into the sea. This eventually leads to her meeting Marin, which leads to Urin releasing Sedna and Kanon becoming the priestess of the sky. Together, they fend off the minions of Sedna to the best of their abilities. Kanon also seem to have the ability to manifest her darker thoughts into a visible aura, which earned her a nickname among her friends and classmates.

Ironically enough, while the old turtle, Matsumoto, often chastises her for this, pointing out that it makes her unfit to be a priestess, that very ability actually made her more resistant to the ill effects of Sedna's presence.