There is a battlefield. Everything is a battlefield. The only light comes in through his eyes, and so it is red, red and fraught with shadows. The ground, that tree, the memory of his mother's face: red.
People passing by: they are red, too. He reads them like charts. This one he can defeat with one move, and an easy one at that; this one he can defeat with one move, but it would need to be a little more elaborate. This one might give him a two-minute fight.
To him, they are all potential battles, and that is why he does not kill them immediately. Some are too weak to be worth the trouble, and others, he wants to save for later.
Sasuke's mind looks like this:
There is a battlefield, but when the light hits it just right, the grass is still green, even if blood has soaked into the earth--and it has. The red comes and goes, and it thrills him when it comes. It brings him closer to--something. He's not entirely sure what.
Of late there have been spectators on the stands, which is strange, because it has been so long since he has had anybody. Sakura and Naruto cheer him on (the latter even when he's yelling insults, because those are better than cheers for motivating him in some ways), and Kakashi stands behind them.
Sometimes he begins to wonder if he could walk off the battlefield and meet them. Did he ever live anywhere but the battlefield? He's beginning to remember that he did. But then he turns and sees his brother on the battlefield again, just out of his reach.
And everything goes red.
Itachi gives the battlefield inside his head as a gift. He does not love Sasuke, if he ever did, but he values him and his potential.
He would have killed his brother otherwise. He did not. Instead, he let him see the beauty of that battlefield.
But in the end, there will only be one battlefield, and it will be his.
No matter who wins their final fight.