User blog comment:Miskos3/Fairy Tail 520: Dragon or Demon, Review/@comment-7418318-20170205011820/@comment-5303512-20170205183554

You do realize that Erza used Dragon Slayer Magic to cut through a dragon's scales right? Not by her own strength and still technically lost.

Well there are no special flames around for Natsu to eat, and I doubt that increasing his strength through the power of feelings will change anything despite Zeref being aware that feelings does effect magic and is immortal, nothing Natsu has could cut him.