User blog comment:FairyRaven/Fairy Tail Chapter 416: Tartarus Arc: Final Part, Review and Commentary/@comment-203.215.121.122-20150121234710/@comment-203.215.121.212-20150125081654

Exactly my point, Lucy traveling to the past to stop Natsu from becoming E.N.D. or whatever. I think that the Eclipse thing from the GMG is foreshadowing what will happen in future arcs, where they will travel 400 years into the past.