User blog comment:Omega natsu2/Chapter 392: You Must Not Forget, Predictions./@comment-2212711-20140706033246/@comment-7418318-20140706080133

Was Lullaby beaten back into flute shape and then sealed up by the magic council again?

If so, maybe it's rotting in some sealed store-room or burried under the rubble of Era without ever being "killed" and thus can't be resurrected.

At any rate if you compare the powerscales of Lullaby (or rather the lack of resilience) I'm theorizing that maybe Zeref didn't create Lullaby as a top-of-the-line bioweapon like the Etherians, but that he was either just playing around or that it was an earlier version of his Demons when he was still learning to perfect his Demon creation skills.