User blog comment:Miskos3/Fairy Tail 520: Dragon or Demon, Review/@comment-5303512-20170204123939/@comment-23853100-20170204145106

Dragon Seed = Dragonification, Demon Seed = Demonification.

I don't know if there's any split personality involved and at this point i couldn't be bothered anymore. But we do know that the seeds represent transformation processes that Natsu is undergoing and Natsu overcame both. So right now Natsu can most probably use his Dragon Slayer magic and Etherious powers at full potential and without drawbacks.