User blog comment:LegerPrime/Acnologia the Ethernano Dragon Slayer/@comment-1776824-20150612174035/@comment-24734624-20150614223838

OK, new theory. Perhaps Acnologia, before becoming a dragon, was one of Zeref's first demons and Mard Geer's brother. Acnologia Tartaros the Angel of Death. The wings in his dragon form were part of his Etherious form. He eventually left Tartaros to find a name for himself while his brother Mard Geer stayed in the dark guild. During the Dragon Civil War, he was taught dragon slayer magic. After using dragon slayer magic too many times, he gets a crazy idea of using Dragon Force while in his Etherious form. That caused him to transform into a dragon. So, maybe his dragon form is a result of using Dragon Force and his Etherious form.