Year X793, Earthland, Guiltina.

Natsu’s group that consisted of himself, Lucy, Happy, Gray, Erza, Wendy and Carla, had made it back from Elentear—an alternate world parallel to Earthland. They were sent here in order to stop Selene, the Moon Dragon God from distorting and absorbing the magic power of Elentear—which they did, or didn’t—because Selene vanished from nowhere, and so did Suzaku, a Sword Saint Dragon Slayer that was powerful enough to dispose of both Natsu and Erza in quick time, which left the members of Team Natsu alone and seemingly victorious, though a bitter victory. They made it back to their own world, in Dramil Town where Fairy Tail temporarily settled, since their main building in Magnolia got destroyed. And after a day of rest—they decided to go back and visit Elsferia—the one who sent them on the 100 Year Quest, in order to report everything that has happened so far.

During their report, Team Natsu has been overwhelmed with tons of new informations that Elfseria threw at them—the existence of a Sixth Dragon God that has already been defeated by Elfseria many years ago whose spirt is laying dormant in a dungeon called the Great Labyrinth, the fact that Diabolos—which Suzaku is part of, is a guild solely constituted of Dragon Slayers whose job is to haunt dragons (which is interfering with Team Natsu’s 100 Year Quest, and at last—the fact that at this very moment, Elfseria had just bee alerted that Diabolos—along with their 4 most powerful members : the Dark Dragon-Slayers Knights (which once again, Suzaku is already part of) are currently invading the Great Labyrinth—in search of Elfseria’s missing heart, that has been eaten by Dogramag, the Sixth Dragon God while he was in his dragon form. Elfseria revealed that his Dragon Slayers element is “Law”, and that whoever finds and eats it in the Great Labyrinth will have access to centuries-worth years of knowledge, enough to defeat the 2 remaining Dragon Gods, Viernes, the Metal Dragon God, and Ignia, the Fire Dragon God. Team Natsu roams through the sky as they look down at the entry of the Great Labyrinth and notices two familiar figures : Laxus and Gajeel—they had seemingly been teleported here by a third party—which is soon revealed to be Selene, the Moon Dragon God, she explains having taken Diabolos over, and her plans of devouring Elfseria’s heart to gain knowledge and location of the human weapon that Elfseria himself doesn’t know the whereabouts—and once she’s done with her monologue, she seals Elfseria away in an instant.

“HEY, YOU! WHAT'D YOU DO WITH GRAMPS?!” Natsu shouted in shock—glaring both in irritation and confusion at Selene. “It wouldn’t do to have him harming himself. You needn’t fear. He’ll be safe until I have the heart. Didn’t I just say? This is all a game. Seven members of Fairy Tail, seven members of Diabolos. A battle dungeon, seven on seven. The first team to reach the heart is the winner." “The hell you will!! I’ll cut you down here and now!!” Erza shouted in denial—drawing her blade, to which her foe answers menacingly. “If you can make it back here with the heart, then I’ll fight you.” “I have zero idea what’s going on, but the point is, we just have to kill the seven people in the dungeon, that right?” Laxus spoke—his eyes already ready for battle. “Having Laxus along oughta make that easy!” “I think you’ve miscalculated, Selene!” Added Gray and Lucy, respectively. “As long as I’m entertained, that’s what matters. Whoever wins—or even if you all die…the heart is mine. I’m merely amusing myself until we find out which it is. The rules are simple. Get the heart and escape! Oh! Two little provisos, though. First, I’ll seal the entrance until one group is wiped out. If you plan to escape, must destroy all seven people on the other team. Second, destroying the heart isn’t allowed, can’t guarantee what would happen to Elfseria, kukukuku! Diabolos is already aware of the rules, and they’ve already started exploring the dungeon, now, let the games begin!” Selene spoke—as she teleported everyone.