User blog comment:Woest/Celestial Spirit King and Zeref/@comment-8153438-20131215082329/@comment-24066070-20131215085716

Zeref's greatest power is the fact that he's the only char in the series who realizes Natsu's ridiculous plot armor. Therefore, he already knows that Natsu will kill him. The reason he cried was simply due to him realizing that he would still have to embark on a war against humanity, since Natsu couldn't end the serie during the Tenroujima Arc. Next time Zeref appears he's gonna tear down the fourth wall, that's how deductive he is.