Dragons

Dragons are a mysterious type of mana-composed beings native to the world of Phantasmagoria. While being absurdly powerful, often times scaling in power to Rank 5 to Rank 4 Eternity Swords, they are also mostly extremely old, holding "unclouded wisdom" in their minds that radiate through their eyes. There is not much information on Dragons as a whole, however it is known by Tokimi and Youita that the Dragons act as Gatekeepers from threats that exist outside of Phantasmagoria, such as Eternals.

Gatekeeper Dragons
Gatekeeper Dragons are the dragons in specific that guard "Gates." Gates, in the world of Eien no Aselia, are ways Eternals or otherwise otherworldly threats can enter another world. With the Dragons in-place, most threats are easily dealt with. Each place a Dragon is home to, a Gate is normally at the same location. However, as Eien no Asliea shows with Takamine Yuuto and the Law Eternals, they are fallible and can let threats slip by.