User blog comment:BlackWizardZeref/Theories on "God Slaying" Magic/@comment-4829046-20131101141300/@comment-24066070-20131101191749

I get your point that kings/sages/extremely talented individuals could be referred to as Gods, but then what would God Slaying magic be? A magic to kill a king? Spells that work exceptionally well against a wise or talented opponent? According to this theory there can be no single definition of a God, as the characteristics which define an individual as a God, such as superior strength, wisdom, leadership, etc would differ between those labelled as a God. Therefore it is impossible to specify anything as God Slaying magic.

Sure enough there can be magic that is effective against a talented opponent, like Aria's Metsu which did massive damage on Makarov as the damage depends on the target's magic power. Following your theory (which is by no means a bad one let me be clear about that) it could be said Aria is far closer to being called a God Slayer than Orga, Chelia or Zancrow.