The Dragon Graveyard!! is an event that takes place during the Grand Magic Games arc.
During their battle with Sting and Rogue of Sabertooth, Natsu and Gajeel begin arguing over their observations of Sting's movements. During their argument, Natsu shoves Gajeel into a mining cart and pulls the lever which makes it move, sending it rolling away with Gajeel inside it, unable to escape due to his motion sickness. With his partner gone, Natsu decides to fight the Twin Dragons of Sabertooth alone as recompense for Sting attempting to do the same earlier on. Meanwhile, a sick Gajeel swears to get back at Natsu for his actions.
Soon after, Gajeel manages to get out of the mining cart once it is knocked over, still angry at Natsu. Unsure of where he is, Gajeel begins walking, knowing only that he is under the Domus Flau. As he proceeds forward, Gajeel comes across an entrance and passes through, finding himself surrounded by the bones of Dragons, littered around the area which he describes as a graveyard for Dragons.
Some time later, Gajeel brings Natsu and Wendy to the graveyard along with their Exceeds. Happy suggests that Gajeel wants to show them something related to Dragon Slayers, while Carla points out that even so, Gray and Lucy tagged along, with the latter stating they were curious. Upon arriving at their destination, everyone looks around and is surprised to see what Lucy describes as "animal bones", though Natsu knows they're looking at Dragon bones and that they're in a Dragon graveyard. As everyone looks around, wondering what could have happened, Happy wonders whether Igneel is among the Dragons, though both Natsu and Gajeel state he isn't since he disappeared in X777 and the Dragons in the graveyard were much older.
Suddenly, Wendy remembers Milky Way, the spell Grandeeney gave notes to Porlyusica about which were then passed onto Wendy. Having initially believed it to be an attack-based spell, Wendy realizes that it may actually be a way to listen to the souls of the dead Dragons. Firmly, Wendy states that if they speak to the Dragons in the graveyard, they might be able to learn what happened to them as well as possibly figure out something about what happened to their Dragons. To use the spell, Wendy begins drawing a Magic Circle on the ground and asks everyone to step back as soon as it is completed.
As Wendy begins her incantation of the spell, a column of light rises from the circle and begins shining as the Dragon bones on the ground begin shaking, scaring Lucy. As she looks for a soul, Wendy notes that the residual auras in the area are old and small but she manages to find one. Putting her hands together, a soul comes forth as she begins concentrating and materializing its form. Everyone is shocked and scared as a large Dragon begins emerging slowly. The smoke soon clears and a Dragon comes forth, getting right in front of the Mages. Seeing their faces, the Dragon begins grinning, commenting on how he likes seeing people's shocked faces as he introduces himself as Zirconis, the Jade Dragon. Noting that the technique that brought his soul forth was Grandeeney's, Zirconis looks around for her.
As he looks, he instead spots Wendy, wondering if she was the one who summoned him. Natsu tell Zirconis to stay away but Zirconis refuses, instead stating he's going to eat her much to Natsu's anger as he gets between them. However, Zirconis begins laughing at Natsu for believing him, stating that he's a ghost and thus can't hurt anyone. The Exceeds then ask Zirconis to tell them what happened in the graveyard and why there are so many dead Dragons. The Jade Dragon initially says he has nothing to say to humans, though they point out that they're cats. As a result, Zirconis begins by telling them that 400 years ago, Dragons ruled the world and lived freely.
In those days, humans were nothing but food for Dragons. However, one Dragon questioned whether Dragons were truly superior and wanted to coexist with humans. These ideals sparked a war between the Dragons who were against him and those two were in support of his ideals. Hearing this, Lucy cautiously speaks to Zirconis, who states he only likes humans as food, causing Natsu to make fun of him for talking to them. Carla asks what happened next, to which Zirconis explains that the war went on for a long time but soon, the Dragons who wanted to coexist with humans taught them how to use Magic to kill Dragons, creating the very first Dragon Slayers. With this Magic, those in favor of coexistence were set to win until the humans turned on them and began killing Dragons, indiscriminate of their standing on the issue. Among these humans was one who killed many Dragons and bathed in their blood, becoming more and more like a Dragon. Zirconis states he was the one who killed all the Dragons whose bones they see before them and that the war that brought him forth was known as the "Dragon King Festival". The human in question is revealed to be Acnologia, who became a black Dragon as a result of his actions.
Everyone is surprised to hear that the Dragon who attacked them on Tenrou Island was once a human. As Zirconis finishes his story of the world 400 years ago, he begins to say something else but disappears before he can do so. The Mages question what happened, stating they still had more to ask but Wendy reveals that his aura vanished completely. Lucy theorizes that he passed on. While Gray comments that they're onto something very big, Natsu asks Gajeel if, by continuing to use Dragon Slayer Magic, they'll turn into Dragons, though the latter claims he doesn't want to.
The Mages then hear from afar that it isn't possible for them to turn into Dragons by the means they heard of, stating that Acnologia is similar to the Demons in the book of Zeref and according to hypothesis, it was the Black Mage who turned a man into Acnologia. The voice reveals itself as Arcadios, who is accompanied by Yukino, the former of whom states that defeating Zeref is the key to beating Acnologia, much to the surprise of everyone.
Arcadios explains that he requires the power of a Celestial Spirit Mage for his plan and so he has Yukino with him. Natsu then confronts Arcadios and asks why he needs a Celestial Spirit Mage. Arcadios then tells Natsu and the rest to follow him as Yukino states that if they go through with their plan, they can defeat Zeref and Acnologia.
The group is taken to Mercurius castle, where the King of Fiore lives. While guiding the Mages, Arcadios reveals that he was the one who orchestrated the kidnapping of Lucy and apologizes for it. Revealing that the Grand Magic Games were established to get power from the Mages of the country, he explains that it was for a project called Eclipse, which required a great deal of Magic. Revealing the Eclipse Machine to the Mages, Arcadios reveals that when the door is opened, one can travel back in time and thus the machine can be used to kill Zeref before he was immortal.