Allegiance are third sphere principalities which are on the seventh rank of the hierarchy of Laguna, the chain of command of the Angels of Paradiso. They are heavily armored centaur-like Angels equiped with a flaming sword that has the ability to be changed into a whip and a shield that can be fragmented and used as projectiles. It is said to appear before humans during times of strife between Paradiso and the World of Chaos to get rid of the evil plaguing humanity.
They appear for the first time in Chapter VII where one serves as a mini boss. After that they are often fought alongside groups of Acceptance and Accolade that serves as their underlings.
Hierarchy of Laguna
"Allegiance belongs to the Principalities, ranked seventh in the angelic hierarchy and part of the Third Sphere. While Third Sphere angels are the most common type encountered in the physical realm, Allegiance, clad in solid gold armor, appears only during times of strife between Paradiso and the human world, in order to purge the armies of evil spirits.
Legends exist of Allegiance appearing before the kings of feudal nations who have prayed for the emergence of a hero; however, there are also stories of Allegiance seeing through the evil in these kings' hearts and instantly reducing their thrones to rubble."
Allegiance's page in the Hierarchy of Laguna book.