Sword aura wasn't something that could be achieved by just anyone, as Ariel had said on the sidelines. It was only something that could be obtained once the swordsman had either managed to understand a swordsmanship style to perfection, or the swordsman had managed to create their own swordsmanship.
The second option was much harder to achieve since you needed to create all of your techniques on your own. However, creating your own techniques also made it easier to perfect them and understand them on a deeper level.
Anyways, both methods were extremely tedious, and sword aura was most likely obtained by less than 1% of the entirety of swordsmen, and even then, it would be something that only swordsmen with YEARS of experience would attain.
However, Art, who was currently on stage, was defying all expectations. Sword aura at the age of 18 was unheard of. Even I never achieved such a feat at that age.
