User blog comment:IamJakuhoRaikoben/Sorcerer Magazine, Issue 48: December 2015/@comment-27298431-20160107184628

I have to disagree about Anna. I think she will have greater importance in the future, especially since Mashima emphasized her existence so heavily at the end 464.

Furthermore, Anna's existence has likely solved a minor mystery from the Tartaros Arc - that is, how come the Celestial Spirit King and Mard Geer are so familiar with each other? It's stated that the two had engaged in battle after MG had obtained the Book of E.N.D. but I'd always wondered WHO had summoned the CSK in the first place and WHY. We now have a named celestial spirit mage from that distant time. Odds are Anna and the person who first summoned the CSK are one and the same. However, the events of 400 years are still being kept insufferably vague so I think there's strong potential for a timetravel arc like in Rave Master.