Board Thread:Episode Discussion/@comment-121.54.103.235-20151215112441/@comment-26397825-20160102004846

The way I figure it is Aura and Soul are not the same thing, but you need to Soul in order to generate more of the Aura. So if they transferred part of Amber's Aura into Pyrrha, Pyrrha would have Amber's Fall Maidens until she runs out of Amber's Aura, which wouldn't regenerate because it has no source. However, if they put Amber's Soul in Pyrrha, then she would have Amber's Aura because the Soul would generate the Aura.

Basically Aura is the electricity and Soul is the battery. You can have electricity without the battery, but it's non-replenishable. In this case, they would put the battery into Pyrrha instead of just the electricity, so the Fall powers are transferred along permanently instead of temporarily.