Betraying the little people who cared for him was the worst decision he made, Sasuke mused.
. . .
When Sasuke was twelve, and betrayed his village, his team, and his Sensei, he did so without a backwards glance. Sure, he felt a little bad about betraying his team, but he was only doing so because he wanted to kill That Man and avenge his clan. Sure, he felt a little bad about KO'ing Sakura when all she wanted to do was help, but it couldn't be helped- she was a liability to bring along. He felt a little bad about using Kakashi's jutsu against a teammate, but was all so he could gain power to kill That Man and avenge his clan.
Sliding his fist through Naruto's left lung made him feel a little more than bad, but the only thought in Sasuke's mind was to kill That Man. In order to kill That Man, Sasuke had to gain power, and what better way to gain power than defeat Naruto, the Dead Last? What better way to gain power than defeat Naruto, who somehow had a special, a secret way of triumphing when he was a millimeter away from death?
What better way to gain power, than to beat his best friend? After all, if he couldn't defeat Naruto of all people, how could he expect to kill That Man? So, at twelve years old, Sasuke proceeded to leave the village with no regrets and no backwards glances.
No backwards glances, Sasuke firmly told himself. He told himself this even though the expression of betrayal on both Sakura and Naruto's face when he KO'd one and nearly killed the other haunted his nightmares.
. . .
When Sasuke was finally away from that blasted village, away from those people, he expected himself to grow strong. After all, he had a mission- to avenge his clan by killing That Ma- no, he would say his name. He would avenge his clan by killing his older brother, Itachi.
Fighting along side Orochimaru (the snake Sannin was terrifying) made him shudder. He didn't have the faith that Orochimaru would have his back as Naruto or even Sakura had. He knew Orochimaru would have no quarrels stabbing him in the back, because Orochimaru had stabbed his own teammates in the back and betrayed them... something Sasuke had done as well.
But when he did not grow as fast as he anticipated, he grew frustrated. Why, why did Naruto grow strong but not him!? Wasn't he the prodigy? The Uchiha? He then proceeded to train himself to near exhaustion. He would attain power. He would kill his older brother.
Naruto's words always came back to him, though- "in order to grow, one must want to protect his precious people."
Sasuke couldn't do that because he'd betrayed his.
. . .
Temporarily fighting alongside Naruto again, after five years of trying to kill him, gave him a peace of mind he didn't know he needed. Fighting alongside Naruto and Sakura was like his senses clearing after a bad case of the flu. Fighting alongside Naruto, Sakura, and Kakashi was like having a brother, potential lover, and parent by his side. Fighting alongside Team 7 to kill Madara was like the old times.
He knew what he had to do after Naruto sealed Madara into an immortal portal of doom. He knew what he had to do when Sakura asked him if he was coming home again. He knew what to do when Kakashi gave him a hesitant smile of gratitude. He knew what he had to do when Naruto thumped him on his shoulder and smiled brighter than a solar flare.
After all, Itachi was still not dead and if Sasuke could not even kill Naruto, he was worthless.
He sliced Naruto's neck with his katana. Among the chaos of defeating Madara, and the War Hero Naruto's assassination, Sasuke had ample time to slip away from Kakashi's lunge and Sakura's kunai.
He felt a twinge of resentment of killing his best friend, but he brushed it aside. At least Naruto died with a smile on his face, in battle- that is what Sasuke used to placate himself. He would kill Itachi now with no problems.
. . .
In the ripe old age of retirement, Uchiha Sasuke softly sighed in regret. His eyes, the ones which he was so prideful of, were faltering with vision. His speed, something he used to kill Kakashi of the Sharingan, was reduced to a wobble as his knobbly knees punished him. His arm that he used to strangle Sakura was now a mere stub thanks to the Fifth Hokage, Tsunade's anger.
His katana that he used to kill Naruto with; however, was shiny as that dreadful day fifty years ago. When he was seventeen and stupid. When he was seventeen and obsessed with power, revenge.
When he was seventeen and the murderer of his best friend, Uzumaki Naruto. Betraying the little people who cared for him was the worst decision he ever made, Sasuke mused. There was no one left to fight him now, no one left to challenge him, no one left for him to call a brother.
The katana was shiny and clean because that was the only thing he took careful care of. The only thing that had last touched Uzumaki Naruto's living breathing body. The source of his regret. The hand that strangled Sakura was decimated, the speed that killed Kakashi was gone, but the thing that assassinated Naruto was still there. A reminder of his stupidity.
Sasuke only hoped his friends would forgive him in the afterlife. With that fleetingly happy thought, he closed his blind eyes and clutched the katana. As he drifted off, he swore he could hear seventeen year old Naruto running towards him, a seventeen year old Sakura, and twenty seven year old Kakashi smiling softly at him.
Uchiha Sasuke officially felt worse than maggots, worse than the bacteria unfortunate enough to be on Madara's skin. His team, the same one who he betrayed, forgave him like the caring people they were.
I thought I'd post the little tidbits of the Naruto-verse running through my mind. These have no particular order and some may not follow cannon.