What type of creature should a Kumiho/Gumiho be?

[MonkeySage]

I've played with different ideas- one of them that a kumiho is what happens when a kitsune dies with ghoul fever. But I wanted to be a little more faithful to the mythology.

A kumiho shares many similarities with a kitsune, but diverges in one way in particular: A Kumiho survives by consuming human livers.

While kitsune and the like are often depicted as morally neutral or ambiguous, as tricksters, kumiho are almost always portrayed as evil creatures.

Given all this, I figure I have a few options: They're shapechangers, cousins of the kitsune. They could also be evil outsiders, possibly demons, which are just often mistaken for kitsune.

[AtlasSniperman]

Given your quick description of the mythos, I see why the ghoul fever option works best.
Perhaps descended from kitsune ghouls? I think there's already a race descended from an undead so it should work, right?

[MonkeySage]

Dhampirs are half vampire- living beings with an affinity for negative energy and vampiric qualities.

And, it doesn't happen often, but when kumiho and kitsune do meet in the same story, they tend to hate each other. Though I don't think that would be part of the myth- kumiho is just the korean version of the nine tailed fox.

[Alabenson]

Just based on my knowledge of the folklore (a kumiho originating as a fox that lives for a thousand years), I'd probably lean towards having a kumiho being either a fey or possibly magical beast with the shapechanger subtype.

[Kaskus]

Overall it feels like a fey to me but starting out as regular foxes seems more like a magical beast. I tried to think of / find an existing creature that began as a mundane animal and couldn't come up with one. I think I would lean towards magical beast (shapechanger) as Alabenson suggested.

[ElFi]

For a comparison, Kitsune in Pathfinder are humanoids by default, but I'm assuming that's not what you're going for here, so skipping over that for now.

Beyond that, I think it depends on what side of the Gumiho you're leaning towards? Their intelligent trickster side, or the liver-eating magical monster side? If it's the former, an argument could be made for making them monstrous humanoids (which have a skills and save progression spread more suitable for trickster-types, in my opinion), though the point has been made that they could easily be anthropomorphic magical beasts or fey as well. And, obviously, they should have the shapechanger subtype (kitsune do as well).

[MonkeySage]

Both actually. Intelligent tricksters with a taste for humanoid liver.

[Kaskus]

ElFi makes a good point regarding the skills / saves. To generalize that, you might consider how you plan to use them in the game to influence their type. Magical beasts and monstrous humanoids are the most martially inclined while fey have a much wider range of skills. I suspect the fey type will mechanically support the mythology better than magical beast or monstrous humanoid.