User blog comment:Miskos3/Chapter 478: Stealth, Review/@comment-4401815-20160320011047/@comment-7418318-20160320080845

He didn't seem shielded in any way when he fought with Natsu.

Besides, why would an immortal who literally can't die, even if you cut off his head need a shield?

If they are shielding anything it's something or someone other than Zeref himself.

Hmm... maybe he sealed up Mavis and Makarov's intelligence and courage. That'd explain why they are so wit- and useless since the end of the GMG.