User blog comment:Relikz/Sorcerer Magazine, Issue 26: February 2014/@comment-3556212-20140303094749

I'll give a puzzle a try...

Answer: Edolas arc

Reason...

I'm assuming it refers to those people who got turned into a giant Lacrima. Since Natsu and co saw the lacrima before they knew it was their friends.
 * Hidden in plain sight

It could refer to Erza and Gray turning back to normal. Earthland wizards uniting, Team Natsu got united.
 * Earthy particles unite

They've prepared their counterattack or the dragon snake thingy. ( ._.)
 * Snake prepares to strike