Conflict on Grimoire Heart's Airship

Zeref's Awakening is an event that took place during the Tenrou Island arc.

Prologue
After Hades is defeated, he, Rustyrose and Kain Hikaru leave Tenrou Island on Grimoire Heart's airship. Rusyrose and Kain comment on how unbelievable it is that they were defeated and on how Zeref and the Ultimate World of Magic was right in front of their eyes, when someone steps into the room. Rustyrose asks who it is, but the mysterious figure just responds that it was people like them that carved him into existence; it was wicked thoughts like theirs that summoned "Acnologia". The three Grimoire Heart members are shocked, while the intruder heralds the end of this age, no one can stop it now, the world will be finished; and Hades mumble "Zeref"

With Zeref standing before him, Hades doubts if this is real or if he is just dreaming and then he just smiles. He orders Rustyrose and Kain to bring him the key, but, with their trembling bodies, they reply that they can't move. However, Zeref says that that won't be necessary as he is already "awake", which makes Hades confused. Zeref asks Hades how many lives he has aready taken in order to get that "key", but then he just says that it's saddening as that is nothing more than an image. He explains that the "key" to Zeref's resurrection was all a lie, as he was never sleep, the one standing before him is the Black Mage Zeref.

Hades screams out that that's impossible, that he had used his eye to see it and that he couldn't even win against one of his underlings. However, Zeref starts unleashing his Magic power, which shocks Hades, Rustyrose and Kain, while he begins to explain his true power.

Assault
Zeref's magical power increases as he explains the effects of his magic and how he is cursed by it. How he is unable to control it when he understands the weight of a human life, and how he is fully able to control his Death Magic when he doesn't care about lives. Hades is shocked that Zeref now fights for the importance of life and he tells Hades that they were the ones to pull the trigger to "Acnologia", which calls for a change of era. Hades asks what is he talking about, Zeref moves his arm in a circular motion while saying that he will bring them punishment. Zeref brings his hands together and says that one of their sins is "Acnologia", and the other is making him forget the importance of life; he tells him to repent and activates a spell.

A concentrated explosion occurs in Grimoire Heart's airship, and Hades falls. Zeref watches as he falls, and Rustyrose and Kain cry out that master Hades is dead.

Aftermath
Zeref, angered, says that "trash that doesn't even know it's trash deserves to fall into the abyss". He then turns around and says that "Acnologia" is here. From the clouds, a large, black, winged beast appears.

Acnologia, the "Black Dragon of the Apocalypse", starts rampaging on Tenrou Island. Zeref stands on the airship watching and explains Acnologia's thoughts against humans, saying farewell to Natsu Dragneel as the current era is coming to an end.