It had been the work of a moment to tear his way through the worlds, following the fading beacon of his creator's power. He had heard the call, faint as it was, and had come, and now it looked as though he was too late. The island lay spread out before him, the giant enslaving tree in the center as always. And he could not detect even the faintest trace of his brother with any of his eight senses.
He felt his eyes go white with rage, and let out a deafening roar at the tiny figures on the ground who must have been the ones to have killed him. Zeref would be happy that he was finally dead, Acnologia knew that, but he is a dragon, not a weakling human anymore, and vengeance is as much a part of dragonhood as mating.
He landed then, surveyed the flies before him. Several of them are dragon slayers, he sees. Grandeeney's get, and Igneel's, and that must be Metalicana's. Pathetic... even the son of the Iron Dragon is small and weak, hiding his fear from the other humans but not from Acnologia himself. He roars again, puts just the tiniest bit of his magic into it, and the humans are thrown backwards from the force like the flies they are.
He plays, then, lets himself go on a bit of a rampage. Most of the humans flee, except for the old one with the refined aura who seems a little stronger than the rest. Grandeeney's blue-haired pet yells something up at him, something so nonsensical that for a moment Acnologia doesn't understand it. Why is he doing this? Isn't that obvious?
Then the little old human becomes a giant and grabs his head, and he is fighting. For a few moments, he feels alive, caught up in the heat of the struggle, but it does not last nearly long enough. The small-large human is not a worthy adversary, for without even using his magic Acnologia has him on his back in a few minutes. He digs his claws into the human's chest cruelly, feels his own magic surge at the man's screams. Not only from Acnologia's claws, but from what looks like recent wounds. So you did indeed help kill my brother, he thought and stared down at his prey. He can feel the rage that is unique to dragons building in his chest, and opens his jaws to crush the man's skull, to claim the vengeance that is his birthright.
And someone is clinging to his leg. His leg. He lets out a roar of anger at the sheer impertinence and tries to shake the human off, but the little creature is clinging like a tick. It's Igneel's dragon slayer; of course that bastard would have passed on his aggravating ways to his pet human.
The sudden bolts of magic from the rest of the guild takes him by surprise, and he overbalances and falls into the water with an immense crash. For a few moments he simply floats underwater, shocked by the fact that humans, humans, managed to push him over. Then he surfaces and sees that that was clearly all their power judging by their depleted auras, and laughs.
And he leaps into the sky, stares down at them from the true place of a dragon—high above the little insects who think themselves so superior—and channels his magic into his mouth. Always a tricky thing to control, this. It always wants to leap and destroy sooner than he would like it, always wants to be a little too wild and fierce to be truly efficient.
The humans have gathered into a circle, clasping hands. Strangely, they no longer seem scared. Acnologia releases his magic—
And the island is gone. Cheated! Some terrible light magic erupted from them in the last moments, so that although the dragon is hovering above an immense hole in the ocean which is slowly starting to fill with water, the true island is not destroyed... merely moved.
Acnologia lets out a terrible roar then, the vengeance-rage slowly quieting in his chest, his eyes slowly darkening to their more normal blue shade. He will return later, and make them pay. When they stop hiding under that alien defensive magic, he will return and avenge his brother. Such is dragonhood.