>>96253078
In ancient times, they were a group of women who were cursed after killing and devouring a Nephil, turned into half-bestial scavengers. Of course, said Nephil had enslaved said women as his harem, so one might say he had it coming, but consuming divinely-cursed flesh and offending heathen deities nonetheless has consequences. Some became violent and feral and succumbed entirely to their curse, becoming the Harpies of legend. The most powerful of these ended up being worshiped (or feared) in their own right as Furies. A smaller number retained more of their intelligence, but were still subject to the same cannibalistic urges, and rather than wandering abroad, used magic to lure sailors to their island, becoming the Sirens.

Of course, as most of the games I run are set in the modern or near-modern era, almost all of the harpies are long since dead or fled. Those who weren't slain in the age of heroes or the classical era ended up retreating to secluded mountain-peaks or isolated islands after the Incarnation, when they lost most of their magic and thus their ability to terrorize humanity.