The kitsune are a Japanese fox-fairies/spirits that are usually portrayed as shape shifting tricksters who can be spiteful, but are usually associated with- if not outright good luck, then at least a sort of benevolent dislike.
Kumiho are not.
Kumiho (AKA Gumiho) are the Korean take on the fox-fairy legend, and while kitsune are more of the 'occasionally benevolent, mostly mischievous tricksters' variety, the kumiho are more of the 'hey, a human, lets rip out its organs and feast on its liver' kind.
The kumiho start off as regular foxes, but after they hit the ten thousand year mark, they sprout eight extra tails and gain some super special magical fox shapeshifting powers. The only catch: the kumiho must go out and eat either human hearts or livers.
Their M.O. tends to be shape shifting into pretty women, seducing men, and then gutting them like fish while they sleep. If fresh meat happens to be unavailable, then they'll settle for going through cemeteries, digging up fresher graves and taking livers from those.
Eventually, a kumiho has a chance to become human. There are, however, a few different ways as to how this could happen.
Way one: a kumiho stops eating human hearts/livers for a thousand days. If it lives, then it loses its fox form and supernatural powers and becomes a real boy.
The other main way? It turns human if it eats enough human hearts/livers.
So it either needs to go cold turkey, or binge out. Or get some magical charm and have some outside help and do some task for some greater mystical being or any number of other things related to specific stories. But in general, it’s pretty much the gluttonous or the anorexic option.
Apparently there's a Korean Rom-Com that ran back in Oh ten actually called My Girlfriend is a Nine-Tailed Fox. Haven't seen it yet, but if they actually aired a guy getting gutted on the night of his wedding by a ravenous fox lady- well, I'd probably have to start watching more Korean TV.