User blog comment:Miskos3/Fairy Tail 525: Why Did the Emperor Never Love His Child?, Review/@comment-4933386-20170304135252/@comment-2214433-20170304140532

The death magic is currently "inactive" because the "current" Zeref isn't in a state that "values life", if he starts caring about life once more, it should pew pew out of him on its own. I don't think it's something that he controls on his own.