User blog comment:Da1337wolf/Dust and Aura, a sudden stroke of genius, bs, or both/@comment-23784953-20130826042041/@comment-23784953-20130826042830

I'd also like to elaborate on the difference between Aura and Dust.

Aura, comes from the soul. Thus, I think them not having any magic circles is correct. Because, you're not casting something if it's coming from your soul. It's like astral projection, but with more barriers and head exploding.

Dust requires magic circles since that's faster than using incantations to cast a spell. Of course, having below average knowledge of magic besides Fate/Stay Night, this logic makes no sense.