Gray Fullbuster has been forced to be on a mission with Natsu Dragneel. This mission was to defeat a group, called Fairy Killer.
This guild was created as they wanted to prove to be better than Fairy Tail, as Fairy Tail has won the Grand Magic Games.
This group wants to get rid of Gray Fullbuster so they captured him to implant a lacrima of the Ice Dragon Slayer magic.
However, being a strong and proud Fairy Tail wizard, he broke free and controlled the Magic, the opposite reaction to what they were expecting.
the story unfolds.