Board Thread:Theories Discussion/@comment-16798306-20130307124756/@comment-6192846-20130307214737

Only reason I doubt your theory, Gear, is because Elluka implies in Wiegenlied of Green that the Demon of Lust was missing from the vessel when she received it and since she may be the one who gave Kachess the Key in the first place, I think she would know if the Demon was killed during The Venomania Event.