User blog comment:Servant of Evillious/Lunacy Novel Tidbits/@comment-12148883-20130901172816/@comment-6192846-20130901175018

That's a good question. At some point, Irina has possessed nearly all of them. Is it possible I.R. gave the Golden Key to Yufina for some reason and then she had Venomania seduce her to get it back? Yufina gave it to Kachess though so her plan fell apart? Best connection I can draw up.

I mean, the Demon of Sin were more than likely created when the Original Sin was split.