User blog comment:FairyRaven/Fairy Tail Chapter 407: All for My Demise, Review and Commentary/@comment-213.89.168.146-20141101142502/@comment-5268982-20141101161058

Yes, I'm with the second anon here. In Tenrou arc, the first time thye met, Zeref sought Natsu in order for the latter to kill him, and he deduced that if Natsu couldn't, no one else could. This is almost proof for me that Natsu is his strongest Demon, and that's why he had so many high hopes from him.