Potential SPOILER:
Huh? I thought she was a demon who possessed Yvonne's body??
I saw someone post it before says Leila is a goddess and she's from the Holy Nation.
Umm... Reading the manhwa... That doesn't seem right... HAHAHAHAHAHHAHAHA. Even in the novel since they didn't really change the antagonist. BUT maybe if they were talking about the OG Yvonne, yes, at least that's feasible... But the thing is, OG Yvonne died very young (I think when she was an infant??). So the demon inside her was there ever since.
BUT DON'T QUOTE ME ON THAT I'm also relying on multiple spoilers lol
In the novel, Yvonne is the goddess Leila, but surely there isn't a goddess creepy as that.