User blog comment:FairyRaven/Fairy Tail Chapter 324: The One Who Closes The Door, Review and Commentary/@comment-112.205.41.120-20130323032321/@comment-6146666-20130323071729

Yeah this is logical. The dark key thing that Yukino has probably has something to do with the demons that were supposed to spawn or whatever. I mean the key itself looked pretty demonic when summoned lol.