Aura is a manifestation of the soul, a life force that runs through every living creature on Remnant, whether they are a meager shopkeep or a renowned knight. However, what sets true warriors apart from all others is their ability to amplify and control their Aura.
Aura is primarily used as a defensive mechanism. Passively coating the wielder in a protective force field, it can protect a combatant from what would normally be a fatal blow. It does not, however, make the user invincible. As they receive more and more damage, their Aura reserve will deplete. If this happens, all the fighter will be left with is his resolve. Fortunately, when a fight turns gruesome, a warrior can also rely on their Aura in a different manner.
"Semblance" is a term used to describe the projection of Aura into a more tangible form. For some this could be the ability to control objects with telekinesis. For others it could mean superhuman strength. The power associated with a wielder's Semblance is completely unique. With enough training and focus, a user's Aura can turn them into something much more than just a man.