User blog comment:IamJakuhoRaikoben/Chapter 359: Fairies Against the Netherworld, Review./@comment-112.205.30.64-20131109154959

Biggest possibility: Kyouka, Jackal, Silver and especially Sayla who possess human appearance are former humans, while the other Nine Demon Gates like Torafusa who has lizard like appearance are former animals that has been transformed into demons.. Just like what is said to Doriate that he was transformed to demon, he is most likely a human beforehand.