Collective term for Azazel, Metatron, and Sandalphon.
They spontaneously turns into Angel under the influence of Uriel's birth. This incident happened during the time between Raphael, Michael, and Gabriel transformation into Angel by Uriel and the birth of the Twelve Apostles. Although the Angel of the End were no match for the Four Archangels, they possess powerful force that surpass the Twelve Apostles.
The twin sister and brother, Metatron and Sandalphon alongside Azazel were persecuted by humans when they were awakened as Angel, and have destroyed a town in the past for self-defense. Hearing about that event, Gabriel appealed to Azazel for serving Uriel, but the negotiation break down. Accompanied by Raphael, the two finally restraint Azazel.
On the other place, Metatron and Sandalphon confronts Uriel and Michael. With no place for discussion from the start, it turns into a clash of power between them. When Michael were cornered by Metatron, she almost imprisoned into the "Adonai Melekh (Prison of the Sinful Angel)" created by Sandalphon, but Metatron and Sandalphon were imprisoned into the "Adonai Melekh" instead due to Uriel's wits. Afterwards, Azazel were brought along and also sealed in the same place.
Even though "Adonai Melekh" is created by Sandalphon's ability, the power of the seal is extremely strong. And it is said that he himself cannot erase it by his own intention.