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.
|B+ Class Mages|
A magical aura is created when the body's container of Eternano particles exceeds the limits of what it contains, or is purposefully released by the user. Upon doing so, the magical energy surges around the body and is exerted outwards in the form of an aura, which holds considerable pressure surrounding it. Depending on the level of magical power one possesses and the control behind it, it can be used as a means to intimidate another individual, or as a preparation for a powerful spell. A single magical aura can have a wide variety of effects dependent on the power an individual exerts.
A Standard Aura (並力の魔霊気, Namiryoku no Mareiki; Literally meaning Magical Aura of Average Power) is produced by mages with a moderate level of magical power within their body. By exerting it outward, it forms a thin layer of pressure that can cause one to be intimidated if they aren't a mage, or if they are a rather weak mage. This is generally demonstrated by individuals of S-Class strength when they are holding back, or when standard mages are showing that they are entering their full reserves of power(B Class mages being the representation of a standard mage). It should be noted that the density of this aura, by a S-Class mage, can cause physical attacks to be repelled with notable ease.
An S-Class Aura (大力の魔霊気, Dairyoku no Mareiki; Literally meaning Magical Aura of Great Power) is one demonstrated solely by S-Class mages or above in potency, and generally are reserved to the stronger S-Class mages as a consequence of their sheer magical strength. When exerted, the S-Class aura takes the form of an overwhelming level of pressure that surrounds the user in a color that best represents their personality. It generally encompasses them in a certain radius, and demonstrates a level of strength that leaves most mages unable to react to it unless they've had continual exposure or exert an aura of similar potency. However, the problem with this aura is that if it used continuously, it can tire an individual. Though considering most S-Class' level of magical power, this is rarely, if ever, the case. The variety of effects achieved by this aura are noted to be quite high, as it can take the form of different shapes and can be used to repel magical and physical assaults alike.
A Monster Aura (未力の魔霊気, Miryoku no Mareiki; Literally meaning Magical Aura of Outstanding Power), as it is classified, is the strongest classification of aura to date. Only extremely powerful mages are capable of this aura, and are generally Guild Aces, if not masters. In the canon, two individuals have shown this aura, notably Gildarts Clive and Makarov Dreyar, both individuals with tremendous levels of magical power. Upon release, the magic almost consumes the user in their color, leaving nothing but a phantom-like apparition to remain. It should also be noted that the aura is far wider, and is generally uncontrolled by the individual.
However, "Monster" auras aren't limited to intimidation, and can be used for the preparation of a spell. This was demonstrated aptly by Jellal Fernandes in his activation of Sema, which caused the environment to become distorted due to the sheer level of magical power concentrated in the atmosphere thanks to his release of power. It is also worth noting that the pressure exhibited from such an aura can form a large column of energy, leaving the pressure enough to visibly cause strain on individuals even from a considerable distance away from the exertion of the aura, indicating at the sheer level of power within this aura. When an individual releases this level of aura, notably Gildarts again, the sheer pressure is also enough to send tremors throughout an entire island, or further, as well as cause destruction to the environment.
It should be noted that mages below B-Class can utilize an aura, however, the effort exerted to do so is likely to expend their power very quickly, making it a rather frivolous thing to do.
An aura is indeed usually generated from a drive, since it is an unlocking of the wielder's full potential, and thus their body usually overflows with Eternano.