Sasuke alone sat in the darkness.
He'd just had Itachi's eyes transplanted, in order to awaken his Eternal Mangekyo Sharingan. He had a lot of time to think for now, as he recovered from his battles with Danzo and then Naruto.
So he sat in darkness, both literal and metaphorical.
He had stopped feeling anything for a long time now. Or maybe he felt so much that nothing registered clearly anymore. He knew the reason for his decisions was revenge, consummately. Vengeance was an emotion, so he must be feeling something. But he had felt nothing when he almost killed Karin in order to get to Danzo. He had felt nothing when he almost killed Sakura, his old team-mate, and comrade, who had professed her love for him. He had felt almost nothing, when his old sensei had tried to talk sense into him, and he had responded with the threat of killing him as well. He had felt something when Naruto saved Sakura in the nick of time, before he could kill her, and then looked at him with that of knowing something. But it was so close to anger (and jealousy), that he maybe he didn't notice.
He had felt something each time, but his anger at the world did not let him recognise, or even notice that he was feeling something.
In fact, he could remember feeling less and less ever since Madara had told him the truth about Itachi. Up until that battle, he had felt terrible anger at his older brother, enhanced by the Curse Mark given to him by Orochimaru. Before leaving Konoha, he had definitely become fond of his team, although he did not always acknowledge it, even to himself. He was settling down into his own life, after four years of loneliness, confusion and the omnipresent hatred of his brother.
The hate he felt for Itachi had given his life a definite direction. Although at one point he had considered staying in Konoha for good, and giving up the path he had chosen, ultimately, he had done what he had always wanted to do. He would kill Itachi. What he was going to do after that, he had not thought of then. In some part of his mind he had considered returning to his village (he had still thought of it as such back then).
So he went off with Orochimaru, whose ultimate motive he knew, but did not care about. As long he got what he had wanted since he was eight.
His childhood, before it burned away with the massacre, had been flooded with a bright, still sunlight. There had still been a few shadows when he had been jealous of Itachi and his prowess, of his father's indifference towards him; but those were the days when he had been happiest.
His days in Team 7 had come close to that feeling, but they weren't quite the same. His rivalry with Naruto, his almost insolent admiration for Kakashi, his annoyance with Sakura for her constant advances, all mingled with some nostalgic feeling of family, made him feel almost normal for the first time in years. But the constant backdrop of his thoughts of avenging his clan darkened everything. And it only got worse after the Chunin exams, with the arrival of Orochimaru. Then, he had been desperately afraid of losing his friends in that fight against Gara. But then the encounter with Itachi, coupled with his growing jealousy of Naruto and his sudden, rapid improvement had pushed him dangerously close to the edge.
Now he could remember, almost apathetically, that he had planned to kill Naruto, but then had decided against it because he did not want to do what Itachi had told him to do.
When he had finally set off to fulfil his one wish he had been grown darker, but there was still some sentiment towards those around him. He thought of team Hebi as his comrades. They helped him reach Itachi.
That was one battle did not want to remember and did not want to forget. It reminded him just what hell Itachi had gone through for him and the village, but it also meant that he remembered that he was the one who had killed that one person whom he had loved, more than anyone else in his life.
He had felt afraid during the battle, and hollow after Itachi died in front of his eyes. It was over.
And then the unbearable pain when Madara told him about the person that his brother had really been. And then the intensified feeling of hatred now removed from his brother and directed towards the people in the village who had ordered Itachi to throw away his life in order to maintain peace in the damned village. He remembered how he had felt, when he had cried for the loss of the beloved brother, as he had cried that night for the loss of his family.
But even as he joined the Akatsuki, now with his new mission of killing the Elders of Konoha, there had been some remnants of human emotion.
He remembered that one moment as it had burned in his mind, when he saw Jugo, Suigetsu and Karin try to protect him, and how Naruto, Sakura and Kakashi had done the same. He remembered Suigetsu telling to them leave as he held off the Hachibi, Karin and Jugo doing all they could to heal him when he lay dangerously injured. He remembered saving Karin, with the same sense of teamwork he had felt for his old team.
But he grew colder. When he heard of Pein's demolition of Konohakagure, he had apathetically assured Madara of his indifference of the fate of the village. It was true then; he planned to destroy it himself.
When he attacked the Kage Summit, convened probably to discuss the growing threat of the Akatsuki to the ninja community, he had not cared about dangerous it would be. The Kages, the heads of ninja villages, were sure to be powerful. He had fought almost all the Kage's present, directed towards them by Zetsu. And this was when he had started to descend into the complete darkness that he now lived in.
He no longer cared what happened to his team, as long as he was able to get to Danzo to kill him. He did not care that Suigetsu and Jugo lay injured as they helped him get through the Samurai and arriving ninja forces.
When he had fought Itachi, what he had felt was a burning hatred for his brother and against what he had done. That fight had been in retaliation against his burning childhood.
His fight with Danzo had been very different. He had still felt that intense hatred, but now it was cold. He had never hated anyone as much he hated Danzo when he told Sasuke that what had happened to Itachi had been no unique incident, that that was the life of a shinobi committed to his village. He had never wanted to kill anyone as much, as when Danzo told him Itachi had made a mistake, that he had shown weakness in letting Sasuke live.
After that, he did not feel much else. Danzo's death had been the only objective in his now cold, calculating mind. He let Danzo think that he had the upper hand, and then attacked him. In that moment, he had been quite willing to sacrifice Karin, no longer seeing her as a person, but only as someone standing in his way.
His descent into something akin to madness had begun there. His irritation with Sakura for her pointless effort, his humourless amusement with Kakashi when he told Sasuke to give up revenge once again, the sudden rush of the old feeling of loss when he remembered just why he was on the path that he was; and then that inexplicable anger he had always felt towards Naruto, revived when he arrived.
He told Kakashi he would stop, when Itachi and his parents, his entire clan came back. When Naruto told him he finally understood why Sasuke was doing what he was doing, Sasuke laughed at him. What did Naruto know of loss, when he had never lost anything?
But then Naruto told him off how he had hated everyone in the village and how he had wanted revenge as well, he listened. He was what Naruto was trying to do and told him how pointless it was. He would never stop.
He would kill every one of the villagers; he would not stop until he had destroyed everything that had made Itachi kill his own clan. Naruto told him he knew that that both of them would die the next time they fought, but at least now they would understand each other.
Sasuke told him he did not want to understand, and that he would not change.
In that moment, he knew that the real enemy was Naruto, because only would be able to stop him, no matter how many others tried. He knew Naruto was getting strong, and that he would have to become stronger to survive.
Itachi and Madara had told him what they had done to ensure the infallibility of their Sharingan. It was an option he had never consciously considered. But now, with his use of his Susano-o ruining his eyesight, and his increased desire to kill everybody that lived at the cost of Itachi's life, and to defeat Naruto once and for all, he made that choice.
He implanted Itachi's eyes into his own.
Sasuke sat in his darkness, with his choices, feeling nothing, but with full knowledge of the consequences of his decisions.