User blog comment:FairyRaven/Fairy Tail Chapter 435 & 436: The Cry of Victory & Memoirs, Review and Commentary/@comment-24228963-20150519060036

My theory is that the story of Fairy tail is just the Book of END being read by Zeref to Natsu Dragneel. But the characters in the story are not actually the real characters. The Natsu in the story is actually Igneel (He was actually a human) and Lucy is actually Layla Heartfilia. Igneel and Layla ended up with each other and they had a child and it was Zeref and they also had another child named Natsu but he died. When Zeref acquired the Ankhseram Black Magic he had killed everyone with it because he couldn't control it. Even his parents died (That is why in the anime Layla and Igneel are shown as already dead). Zeref revived Natsu so he would still have family with him but knowing that his magic may kill him he turned him into a demon so he wouldnt be affected. He and Natsu are the only ones alive in the world. Zeref's END book contains the stories that were told to him by his parents. He changed the characters so Natsu wouldn't wonder who were the characters. In the story, Zeref is shown as the most evil wizard because Zeref in the real world killed everyone. Mavis is actually Zeref's Light and Acnologia is his Darkness. The whole story of Fairy Tail is actually just in a book that is owned by Zeref and he is telling these stories to Natsu. Zeref and Natsu's story is set in the future and the one shown in the anime are just the stories of their parents which is set in the very very far past.