User blog comment:IamJakuhoRaikoben/Chapter 406: The Girl Within the Crystal, Review./@comment-117.205.5.87-20141028094333/@comment-31.132.65.60-20141028133042

Or maybe Mashima has no conception for the story and just writes his manga from chapter to chapter, since it was first said that Mavis grave is on Tenrou Jima and that where her ghost was, now it turns out that she is alive in stasis underneath their guild. And Mashima won't even bother explaining this, because he will leave it (like many other things) for the fans to explain themselves.