The Ascension Form is a special power possessed by angels which allows them to release their full angelic power inherit within them. Once activated, the Ascension Form reveals an angel's true visage and being, and in the process amplifies their physical and magical attributes. While a lone angel is already formidable, their Ascension Form makes them even more dangerous, for once they manifest this power they can also have access to additional powers and abilities that are stored within them. Ascension Form is basically the opposite of the Devil Trigger, which is a demon's special power.
An angel can release their Ascension transformation only when facing an opponent that surpasses their physical prowess and proves to be a threat. The downside of this is that an angel is prohibited from using their Ascension Form when in proximity to humans, as their true forms are so overwhelming they can literally burn a human's eyes out or even to the point where it can be fatal to the human. Demons and monsters can even fall prey to the intensity of their true visage. Thus, they are required to move the threat far away from the humans in order to unleash their Ascension Form without any collateral damage.
When in the process of activation, an angel is coated in a large spectral multi-eyed and multi-winged angelic being before being engulfed in a brilliant white light that soon dissipates and reveals their true angelic form. The size of an angel's true form reflects upon the amount of power they weild. For example, an angel with the status of a Power or a Dominion possesses a form which is said to be as large an apartment building, a Seraphim can be the size of the Empire State Building, whilst archangels can reach a magnitude that exceeds of that of mountains.
However, when the usage of this ability concerns the archangels, they are completely forbidden from using their Ascension Forms while on Earth for it is said that should they utilize their full angelic power, they could potentially render an entire city or even half of a continent to a cinder. Thus, they are only allowed to use the full brunt of their angelic might in Heaven or on another uninhabited planet.