Illyria is ... hard to explain. She's an "Old One," one of the demons that predates humans, also referred to as a "God-King." Who got brought back in a human body. And she has an Anya-esque confusion about all things human. And she's decided Spike is her pet. And ... that just doesn't even begin to explain it all. *waves in the direction of Angel Season 5* Very hard to explain.