"Supernatural" makes more sense, I agree, but "spectre" had a better ring to it and rolled off the tongue easier. Same with "malefic", though I do appreciate the aliteration with "beguiling". Maybe "Alluring Black Crystal" or "Bewitching Black Crystal" would've worked better.
While specter sisters is something I am used to, I can agree on supernatural as closer in meaning. They are putting a lot of effort on the translation. I really like the idea behind the beguiling Crystal and the way it was explained by them. They are really creative as translators and I really hope I wll be able to sell my old box sets so I can start collecting these.
I like "Beguiling Black Crystal" a lot more than "Malefic Black Crystal" (but personally I'll go on calling it the Grim Crystal).
I never liked "Spectre Sisters" (especially since it should have been "Specter Sisters" given it's a US translation) and I don't like "Supernatural Sisters" either. To quote my own blog, here are my thoughts on the matter:
In Japanese folklore, ayakashi refers to any supernatural entity . . . that “appears above the surface of some body of water.” In many stories, they are “the vengeful spirits of those who died at sea,” but in others, they are simply atmospheric ghost lights, a phenomenon often associated with UFO sightings . . .
Given there’s nothing remotely nautical or maritime about the Four Sisters, it seems doubtful [Naoko] intended to reference vengeful sea ghosts with her use of ayakashi. With UFOs, crop circles, and related phenomena at the center of the Black Moon Clan arc, it seems far more likely she was referring instead to atmospheric ghost lights.
For this reason I think the best way to translate Ayakashi no Yon Shimai would be with a word that evokes that connection, that evokes the experience of witnessing that strange and mysterious phenomenon. “The Four Eerie Sisters” is probably the best option, with “Uncanny,” “Unearthly,” and “Otherworldly” being good possibilities as well.
"Beguiling Black Crystal" makes it sound like a silly name that no one would ever take seriously. "Beguile" is one of those Oldworldian words that no one ever uses in normal dialogue, only ever really seeing use by those who are specifically trying to sound hammy and overdramatic for comedic purposes. And the alliteration in this case makes it sound even more goofy, when it's supposed to be, yannow, a weapon of mass destruction meant to commit genocide by a kingdom of terrorists.