Disclaimer: I don't own Naruto, obviously; I don't even know how the battle actually went, though I do know the outline of it. (This fic is AU.)
Catalyst
He thinks he can hear the voices of the angels call to him; he cannot be sure, for a violent mantra thrums in his ears - a mixture of his heart beating in his throat and screaming. He is fairly certain it is not him who grinds out the hoarse screams, because it does not sound like his deep baritone.
He knows, even though his eyes are going blind: both of them are mere steps from death, but he lies closer.
He gazes, face schooled to be as blank as a slate, into his brother's face; Sasuke's red eyes spin wildly with rage, but a triumphant look frames them. Smug; I have caught up to you, brother, he can read in the expression.
The seventeen year old is so very clueless.
So very clueless to how far Itachi had gone, simply to ensure his younger sibling's safety; selling his soul, marketing a life that had so much ahead of it … for a life that would be wasted away, a life powered by a black heart set on the path of revenge. But it was - no, is Itachi's set up; by taking himself out of the picture, Sasuke will perceive himself to be living in shadows no longer, and he can live in glory, to live to boast that he slew the brother who killed their family and never looked back.
His brother is naïve, even; he has grown physically, yes. He towers over his older brother, giving the imposing illusion of superiority; but an illusion is naught but an illusion, and illusions set perceptions of reality askew to the clueless. Sasuke is still the insecure, hopeful little child that he has known all along. He has tried to grow out of it, of course; but one glance in those bloodlust emblazoned irises and deep, sorrowful hurt makes itself evident. His mission is that of a brave man's; his motivation is a damaged child's. The obvious rift between the ambition and the drive is evident.
His heart slows in its beats, and blood drips down his chin. He closes his eyes.
His brother has fought long enough. Who is he to deny his dearest little brother anything? Let him have his revenge that he set his heart towards; let him have the vengeance that touched the lives of more than one with hurt. He wishes to see his clan in Hell; yes, he murdered them, but they were no more innocent than he.
He would have died eventually – Sasuke was merely the catalyst.