User blog comment:GrandChariot/About Natsu and E.N.D/@comment-87.202.68.135-20150120180718/@comment-25572451-20150120231050

^^this, and what's not to say that natsu and zeref couldn't have been friends though he was a child. Zeref was close friends with Mavis as well, and they met when she was 12. Maybe instead of Zeref sending Natsu to the future, perhaps all the 1st and 3rd gen dragon slayers were originally from 400 years ago, but were all sent to the future by their respective dragons for the sake of taking down Acnologia. Which may explain why igneel butted heads with E.N.D because he sees it as an abomination taking the form of his foster son.