Should add onto the list: "Souls, Space, Dimensions," for Affinities that have also been rejected, and I get the feeling that it would also be necessary to preemptively tack on, "Time, Mind, Life, Force, Fate, Matter, Void."

Going back, I still feel that an "Ephemera" Affinity would probably work best for what I'm trying to achieve within the boundaries of the setting. Spells relating to spirits/ghosts without directly correlating to either. It's not necromancy, and it isn't "an entire class of beings," though honestly that parameter is kind of vague.