Fallen Angel

The Fallen Angels (堕天使 Datenshi) are one of the Three Factions in High School DxD, alongside the Angels and Devils.

Summary
Fallen Angels are Angels that have fallen from the grace of God, due to having "impure thoughts" that divert them from the teachings of the God in the Bible. The leaders of Grigori were tempted by human women and had fallen after having sex with them.

Despite being cast out of Heaven, Fallen Angels and their subordinates have been known to occupy churches and use them as bases. However, they go out of their way to destroy all of the religious icons in these churches in the process.

Currently, the Fallen Angels have the smallest population among the Three Factions.

Appearance
Fallen Angels have an appearance similar to their Angel counterparts with their wings; however, their wings are colored black as opposed to the Angels' white wings. Also, because they have been cast out of Heaven by God, they also lack the halos above their heads. Fallen Angels are often seen wearing dark-colored clothes, mainly pertaining to the colors black and violet.

Like their Angel counterparts, the rank of a Fallen Angel depends on how many wings he/she has. For example, Azazel, the leader of the Fallen Angels, has six sets of wings which justify his position. The blackness of the wings of each Fallen Angel is also different, Azazel, for example, has jet-black wings with feathers that have the color of everlasting darkness and is darker than endless darkness.

Abilities
Although they have been cast out from Heaven, Fallen Angels retain the ability to use light-based weapons. This type of weaponry is extremely harmful and poisonous to Devils, as it is shown many times when Issei is wounded by Dohnaseek and Raynare.

Unlike Angels and Devils, who require the use of a respective Brave Saint or Evil Piece to replenish their numbers, Fallen Angels can replenish their number of "pure" Angels simply by tempting the remaining pure Angels in Heaven to join them. It is unknown if it works in the opposite direction, where the Fallen Angels can redeem themselves via selfless and righteous acts to rejoin Heaven. They can also increase their numbers through childbirth, as with the case of Baraqiel with Akeno through Akeno's mother.

Fallen Angels, like other factions, have their own system of magic and spells. This includes a method to wipe the memories of large numbers of people, as shown when all of Issei's friends forgot about Yuuma, or when Azazel wiped the memories of the girls of Kuoh Academy.

Grigori
Grigori (グリゴリ Gurigori) is an organization created by Azazel and the Fallen Angels who fell with him. The members of Grigori include exiled Church members (Valper Galilei and Freed Sellzen, for example) and Sacred Gear wielders. The leaders of Grigori are Azazel, Shemhazai, Baraqiel, Kokabiel, Armaros, Sahariel, Penemue, and Tamiel.

During the Great War, Grigori was the first to retreat after losing most of their forces, except for their leaders. Ever since then, Azazel has become more peaceful and tries to avoid battles as much as possible. However, there were still small fights between the Fallen Angels and other factions which did not reach Azazel's knowledge. An example was when Raynare and a group of Fallen Angels acted behind Azazel's back and performed a ritual to steal Asia Argento's Twilight Healing.

In Volume 12, Azazel reveals that Grigori lost more of its members to the Khaos Brigade after a group of top-class Fallen Angels had been discovered to be giving out information to them. Due to losing more of its top-brass members and the decreasing rate of natural-born Fallen Angels, Azazel says that Grigori might meet its end soon.

Trivia

 * Grigori is an alternative name for the Watchers from the Book of Enoch. Also, the leaders of Grigori are all Fallen Angels from the Book of Enoch.
 * Azazel mentions in Vol. 8 that female Fallen Angels possess seductive bodies in order to seduce men.
 * This is true with Raynare and Kalawarner, who are pure Fallen Angels, though some of the female Fallen Angels (like Mittelt, for example) are still developing, implying they have different growth rates.
 * Azazel has stated that, even for a Fallen Angel, Akeno is particularly seductive.
 * Samael (the Dragon Eater) has the upper body of a Fallen Angel.