Mask Magic

Mask Magic (仮面魔法, Kamen mahou) is a Caster Magic often used in conjuction with Summoning Magic that allows the user to dawn a mask that will grant them great power. Often referred to as Masks of Rebellion, these face ornaments allow the user to temporarily break free from the chains of their humanity to utilize the power of the beast or monster whose mask they wear. Masks are either earned by or granted to users via the defeat or the forging of contracts with beasts and monsters as the souls of the creatures are what take the form of these masks worn upon the users' face.

Overview
Mask Magic is a form of caster magic that is often used in conjuction with Summoning Magic that allows the user to dawn a mask which grants them great power. These masks are often referred to as Masks of Rebellion as they allow the user to break free from the chains of humanity for a short time to utilize amazing and sometimes deadly powers. Similar to Take Over in a sense as the masks are formed as the physical manifestations of the souls of monsters and beasts that are either defeated or contracted by the user. This being the reason it is so often used alongside summoning magic as those creatures are already contracted to the user and thus can take the forms of masks when fighting alongside their master is not possible. As stated before, masks are the physical manifestations of the souls of different beasts and monsters, these masked being gained by the user when they are able to defeat a powerful beast in combat, stealing their soul as it permanently takes on a mask form or through contracts formed with those same beasts or monsters in which their souls can be borrowed for a short time, manifesting in mask form and being worn by the user. Upon dawning one of these masks, the user is allowed to utilize the strength, power, and magic of the beast whose mask they wear. Breaking free from the limits of their humanity to give them strength and speed unthought of to be wielded by the fragile bodies of humans. Effectively, they are rebelling against those limitations and taking on the power of monsters and beasts. However, this power does come at a price, breaking free from those limitations can have negative effects on the body, even upon taking the form of the beast the user will have to deal with the consequences of pushing themselves once the mask has been removed. These consequences often lessen over time as the user advances in the magic and trains their bodies to handle to abuse wearing one of the masks deals out but regardless the user may still feel sick upon removal. Forcing the body to continue using the masks beyond their allowed limit is still known to cause devastating results which is why it is in the user's best interest to remove the mask before that limit is reached to avoid that possibility altogether. While it is all but impossible for an opponent to rip a mask from the user's face, the user themselves can easily remove the mask. Souls that are burrowed can only be utilized for a limited time regardless of the user's proficiency in the magic as not only does it strain their own body but the that of the creature whose soul they wield. Taking on the form of the mask is a difficult task that requires an immense amount of will and trust in the user but despite all of that, their ability to remain in that form is limited as their soul can only produce so much power before the threat of it being snuffed out becomes a real danger. Beasts whose souls are stolen also have a finite amount of energy as the soul is no long attached to a physical body and cannot be replenished and thus will disappear once the entirety of the soul has been used up. When either of these two things occurs, the mask will crack and begin to flake away into the wind. Having this happen in the middle of battle can have deadly consequences and as such, it is important for users to understand and keep track of the time they can utilize with each of their masks as every soul is different.

Trivia
This magic had several inspirations stemming from the Persona masks from the Megami Tensei Persona series, the Visored from Bleach, and even a little bit by our very own Lady Komainu's Beast Embodiment which is admittedly is much better than my own and should defintely be checked out.