The Daeva's powers comes from their ability to control Aether, which very few Humans are capable of (even most Humans who are able to control Aether do not achieve ascension).
Of all the feats that the Daeva possess through controlling Aether, the most notable one is the immortality of the Daeva. While their bodies may temporarily be slain by a fallen blade or a well-aimed arrow, the spirit may revive the body with the power of Aether to become whole again. They are not everlasting, however, as they could become "lost" by falling prey to the depths of The Abyss. They could also become "banished" to forever wander the earth as feeble spirits.
As Demi-Gods living among mortals, the Daeva are revered and given the unchallenged right to rule over the Humans. With power comes responsibility, and it is up to the Daeva to protect the Humans from attacks of other races.
The Daeva had been entrusted with the responsibility of protecting the Tower of Eternity. However, after the Millennium War, the Daeva split into two Factions, the Elyos and the Asmodian. Following the destruction of the tower the two factions were separated, each occupying a different half of Atreia, and only recently have they rediscovered each others existence. In this discovery they have become locked into a blood feud as they each hold the other faction responsible for the tragedy. Moreover, the emerging problem of Aether disappearing into The Abyss may spell an end for the Daeva.