User blog comment:Udarsha45/Bleach - The Dagger/@comment-1268838-20130829050631

It would seem that we have confirmation that Aizen is a Special War Power, and that there is no differentiation between those for the Wandenreich and Soul Society - they are simply assets that could help either side. Hence why Yhwach went out of his way to try to recruit Aizen and capture Ichigo.