Sasori had never been the type to do anything stupid in desperate times. He knew people who did – he knew people who cut their arms open or stopped eating or, god forbid, jumped off of bridges to stop the pain. But he himself wasn't like that. He had suffered, oh yes. He had lost his parents, his village, he had lost everything. Still, he carried on. Things got a little murder-y the longer he stayed by himself, but he never, ever harmed himself.
He thought his puppets would save him. Turning loved ones into pieces of wood or plastic should have helped him. He wanted to become stronger, and he refused to accept his lust for blood was because of his dead parents. So many people died by his hand. So many bodies to practice on.
He didn't understand why the hurt wouldn't go away. How many years had it been now, since his parents died? He had been nothing but a child when it had happened. Yet, still, it haunted him, and he couldn't take it anymore. He felt too much pain. It needed to go.
Still he refused to hurt himself. What would that achieve? Nothing. It wouldn't bring his parents back. It wouldn't undo every bad thing he'd done in the past ten years. But the hurt was unbearable, and he had to do something about it.
It was a warm day in the middle of the spring. He was carrying the body of a high class shinobi from the Sand back to his temporary hideout when the idea hit him. Perhaps the only way to cure himself of the heartache was to remove it all together. He had seen people do it before, turn their limbs into plastic, puppet limbs and live to tell the tale. His grandmother had modified her arm, surely he could do the same. Except he didn't want to change just one limb. He wanted to completely transform himself.
It wasn't an easy process. He was too vain to let himself die, and he wasn't going to lie to himself. He feared death. Everything had to go perfectly. He started experimenting on live people, kidnapping them and trying to keep them alive as he changed them from human to puppet. Every failure resulted in a loss of hope and shameful nights crying himself to sleep, but every now and then he managed to make some progress.
It wasn't difficult to replace an entire body with plastic. The hard part was keeping the brain and the heart working without his subjects turning into robots or dying within hours. That was seemingly impossible.
He had started experimenting on himself, too. His skills as a shinobi had never been that impressive, the only thing that made him strong were his puppets. He was simply too vulnerable if he was weaponless. As time went by, he started to feel the need to become the most overpowered puppet in shinobi history.
It took him two years to finally manage the transformation. It had been a stroke of luck, really. All he wanted to do was see what the effect of his new poison was on the human body. He hadn't expected it to change his subject entirely.
It was ironic, really. The only way to get rid of his feelings was to poison himself. He laughed at the mere thought of it, but it wasn't funny in the slightest. He knew how to complete the operation now. There was nothing left to stop him but his own consciousness. He told himself he could leave it until later. There was no reason to do it straight away. He could wait and see if he still wanted this.
By that time, he had already joined the Akatsuki. He had lost to Konan in a stupid battle a while ago. They planned to take over the world in some ridiculous way. He wasn't even remotely interested, but he pretended he was. At least they took away some of the loneliness. However, they were somewhat obsessed with their plan to rule the land, and it annoyed him. He decided the loneliness was better than this insanity.
They decided he had to stay.
Itachi's Tsukuyomi was something Sasori never wanted to experience again. It had thrown him straight back to the day his parents died. All the feelings he'd tried to suppress were forced onto him for hours on end and there was no escape, none whatsoever. By the time it ended, they left him to deal with it by himself.
He was too weak, he needed to be able to defend himself from anything life could throw at him. Enemies, friends, his own emotions, he had to be stronger than it all. It was that night that he changed himself forever.
His body was already partially immortal, so that had saved him some of the work. But desensitizing himself hurt, and it hurt a lot. He should have known to expect this, but as he lay on the floor with the poison coursing through his veins, howling and yelling in agony, he told himself that it was worth suffering for a few hours if it meant he would never feel pain again. He thought of his parents, how much he loved them, how much he missed them. Guilt swept through him – would he forget them if he lost himself? It was too late to stop what he had done in the heat of the moment, and now he would lose them forever. He had never stopped to think about the fact that they lived on in his memories.
He blacked out at some point, accepting that the poison had probably killed him. He couldn't remember how much he had used, it had all been a blur of panic and rage when he came back from his encounter with the Uchiha. Perhaps he didn't want to wake up. No, it wouldn't bring his parents back, but what was left of his life now? What could he possibly have left to fight for?
Fate, however, was not that kind. He found himself awake after days, perhaps. He couldn't tell. His entire body was now made of plastic, and he felt strangely apathetic. He sat up, moving almost instinctively, disconnected from reality. He vaguely remembered panicking before he fainted, but it all seemed like a distant memory.
Here he was, sitting in his workspace, among his huge collection of puppets. He looked up, coming face to face with the puppets he'd make out of his parents' bodies. He blinked. Something told him that should mean something to him. He still held them in high regard, but the sorrow he'd once felt at their loss was gone. Unreachable.
It surprised him that he'd managed to hold onto his consciousness. He still had no desire to conquer the world with the Akatsuki, but in his quest to become the strongest it seemed reasonable to stay for a little while longer. It was time to return.
He was liberated as he walked over the dry sand towards the Akatsuki's current hideout. The poison had eliminated most of his emotions, but he'd be lying if he said he felt nothing at all. It had numbed him to his past and shielded him from the future and the present. He simply no longer cared about anything, all he could think of was the one thing his old self had left him with before he'd turned into this monster. He had to become the strongest.
He didn't know why. He didn't understand. But, whatever the reason, it gave him something to hold on to. He was immortal now, with the capability to live well over the lifespan of any normal human. He needed a purpose.
As he continued his journey with the Akatsuki, he noticed there was still an inkling at the back of his mind whenever he had time to think, whenever he was by himself. Something not even the poison had been able to completely weed out of him. He continued to modify himself, to make himself the strongest weapon in his arsenal. All driven by one, carnal emotion.
Regret.