Angels can mostly be found in the Abrahamic religions, but also in Zoroastrianism, Sikhism and Theosophism.
High School DXD
One of the three Supernatural Factions in High School DXD, along with Fallen Angels and Devils.
Originating from Heaven, the Angels are powerful beings who serve the Biblical God, and have the powers to inflict pain upon Devils/demons due to their light-based powers. Unlike Devils and Fallen Angels, Angels need to purify themselves when having sex and both the Angel and partner must undergo a lengthy purification ritual (it takes several hours). They must also need to do it inside a specially crafted barrier and they both must not harbor any kind of negative feelings while doing it, rather it must be done out of pure love.After the death of the Biblical God in the Great War of the Three Factions, the Angels were incapable of increasing their numbers normally until the creation of the Brave Saint system which allows the Angels to reincarnate humans into Angels.
It is revealed that there are also traitors in the Heavens who were giving out information to the Khaos Brigade. Ironically, these top-class Angels were able to do so without falling due to a loophole in Heaven's system. These Angels, however, became Fallen Angels after leaving Heaven and joining the Khaos Brigade.