The Aesir are a group of beings, that have subtly influenced the Thyran races in the past. Each major race has its own guardian deity. The canines worship Tsukiyomi, felines revere Kagutsuchi, while saurians venerate Hoori. There is also an unknown "Fourth One". The Crystal Guard is both the Aesir's public face and the enforcement organization, if need be. 
Great Race War
Through unknown means, the Matriarch set the feline-, and the caninekinds free from the Aesir influence and unleashed the Great Race War on Thyra. The worship of the Aesir is banned on the realm of Vanaheim.