User blog comment:Miskos3/Fairy Tail 525: Why Did the Emperor Never Love His Child?, Review/@comment-1359322-20170304144018/@comment-7418318-20170304170828

If you compare the attacks that Zeref launched against Natsu and the one he used against Larcade, I'd say that Zeref didn't actually seriously try to kill Natsu (yet), but got so caught up in the "fun" of the fight that he just wants to enjoy himself some more.