Maryoku no Reiki
A Magical Aura (魔力の霊気 Maryoku no Reiki; Literally meaning Aura of Magical Power) is a common term given to the exertion of magical energy into a form outside of the user's body that isn't used in the formation of spells. It has been demonstrated by various mages of varying potency, and is a common means of intimidation when focused.
Those who possess Magic have connected their physical spirit with the spiritual flow of nature — Eternano. Consequently, this connection is passively manifested outside of the Mage's body as a constant exertion of power, for such connections are unable to be isolated within the body. For the most part, Mages who casually exert their power in this way do not interrupt their surroundings or individuals around them. This allows them to coexist with normal Humans without any restraint.
However, to those who possess power far beyond compare, such as individuals of the Spriggan 12, even passive exertions of their power are considered to be monstrously overwhelming to those of a lower class. When achieving power at this scale, only individuals with similar power or constant exposure to such strength are able to withstand their company. That being said, as only the passive outflow of one's magic from the body, this sort of exertion has no effect on the environment despite the magnitude of strength the individual may hold.
The magnitude of an aura's effect on the surrounding enviroment is relative to the base level of power that an individual holds at a given moment within their body. Those who do not possess high levels of power will find their aura barely surrounding their body in a thin layer, and having minimal effect on the people and environment around them. Those with stronger auras may have their power exerted in manners that even cause physical destruction should they not keep their strength in check.
An aura, as a whole, does very little in a combat sense. It gives awareness that an individual is using their power, and gives an indication as to how much power one is attempting to exert at a given time. This only holds true for those who do not possess a huge well of magical energy. Individuals such as August, who possess enough magical energy to allegedly destroy a country, can exert their power with such strength that the very air and ground begins to shake.
Although directly manipulating one's aura for combative purposes is possible, the strength that a "byproduct" of one's magic possesses is minimal compared to the actual reserves of magical power within them. As such, its major use may be to deflect minor attacks, or be used as a way to sense the position of other mages by feeling out "interfering" auras.