It is said that a Semblance is the extention of one's Aura. Unlocked through either extreme circumstances or discovered through training. It is the physical manifestation of one's soul. Their ideals given form.

An Assassin appeares and executes the Queen of the Grimm. He does not elaborate and then leaves. (One-Shot)

Jaune Arc desired to be the best Huntsman he can be. While training his aura, he finds it in the discovery of his Semblance. (One-Shot)