User blog comment:Omega natsu2/Chapter 371: Tartarus Arc, Part 2: Song Of The Heavenly Dragon, Predictions./@comment-7418318-20140207110431

Fairy Tail I'm a bit torn on the motive. She could believe that Mira doesn't deserve to become a Demon, she could believe that there's too much of a risk of Mira turning her newfound powers against Tartarus or she could just intent to torture Mira for fun and to get back at Fairy Tail.
 * Minerva will break the tank in which Mira is being held, thus preventing her from being turned into a Demon.

Magi This valley had unnaturally high and steep walls and due to being so wide, sunlight should reach the bottom, but it doesn't. There is a complete absence of light despite there being nothing to block the sun. So I think this "valley" is really something like a crater from the event that wiped out Alma Toran and that the darkness is caused by residues from the magic that was unleashed in the war.
 * Alma Toran used to be in the place where now the massive dark valley is, in which Junan has his home.