A/N So I was recently introduced to the world of Doctor Who, and I must say, I've become quite obsessed. This is my first attempt at doctor who fanfiction and I'm very excited.
This takes place during the episode titled Dalek of the first of the new series. It happens directly after the Doctor shuts down the vault with Rose inside and he hears the Dalek say exterminate.
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The Doctor yanked out his ear piece, fighting with the overwhelming sadness that overtook him. Tears pricked at his eyes as he slowly turned.

"I killed her," he whispered to himself, wanting nothing more than to be dead himself.

Rose was gone. She was like a bright star that had come so suddenly into his life, and now just as suddenly she was gone. His hearts screamed in agony at the thought of being alone again, at living without Rose by his side to hold his hand, and give him a feeling of rhyme and reason in his chaotic world. The one person he cared most about in the entire universe, in all of space and time, and she was gone. How could he live with himself, knowing he had killed her? It was the time war all over again, except this time, he questioned his decision. Was it really worth it? Was it worth Rose? His whole soul sadly told the answer he already knew. It would never be worth it. Because his world without Rose wasn't worth living in.

Yelling at Vanstaten should have made him feel better, but the Doctor only sunk deeper into his grief. More and more thoughts flooded his torn apart mind, more and more regrets, more sorrows. She had only been 19. 19 years old, and now she was dead. Jacky was right to mistrust the Doctor. Because of him, Rose would never again return home.

Then to top it all off, Adam entered the room, bringing a fresh wave of emotions with him. The Doctor felt a surge of anger towards the man that surpassed all reason. It was an irrational anger, even for him. There was nothing Adam could have done, but somehow that fact that he had survived and Rose hadn't made her loss that much harder on the Doctor.

A noise from the screen caught the Doctor's attention, distracting him from the unfounded anger. He gazed up at the screen, a feeling of wonderment blooming in his chest. Rose! She was alive! She was alive, and the whole of creation seemed to be singing with joy. Hope burned in the Doctor's chest as he looked at Rose, scared but alive just the same. As long as Rose was down there, he knew, he knew, he could conquer the Dalek. He could defeat the entire Dalek race, the Cybermen, the Master, and every other foe combined if it were for Rose. For her, he could and would do anything, anything at all.

Even the chill that swept through him as the Dalek spoke couldn't kill the hope shining within him. Just to hear her voice was enough to keep him going. Yes, it scared him to hear the Dalek voice the feelings of his heart that he had tried so hard to deny and to hide, but if anything, it made the Doctor's joy so much more complete. Was that the reason his sadness had seemed so great and his happiness so full? Was it because he loved her? Yes, his hearts answered. Yes, a thousand times, yes. And it was because of this he had to open the vault. He killed her once, and it was physically beyond his powers to do it again.

In fact, he would go to great lengths just to ensure she lived. To go through so much and loose her now would be too much. And so for the first time in nearly a lifetime, the Doctor held a gun in his hands. It felt wrong, and it felt like the time war, but it also felt like life, and like love for Rose. Because of him, she wouldn't die, but live. He never anticipated she might not need saving.

To see her there standing in the way of the Dalek, struck something deep within him. And her words… he felt the brightness of hope leach away from his body as he took stock of himself. Was he changing again? This time for the worse? Was he reverting back to the way he was directly after the war? He knew as he saw her there, with her kind and open heart, willing to love that creature even after it threatened her, he could never let himself become that man again. Not when he was with Rose. She was too good for him to let himself slide into the war hardened man he had been.

But the Doctor knew, even as he knew many constant things about the universe, he knew that it wasn't even possible to become that man again as long as Rose was with him. She was changing him, just as she had changed the Dalek, something he had never thought possible. Rose was a miracle. A soul so beautiful she could change the universe for good. So beautiful, she could change him into a better man.

After it was all over, the Doctor approached the Tardis with Rose beside him as sadness filled him again. This sadness was different though, less sharp and agonizing, more deadened and dull. He was alone in the world, the last survivor of the time war. But as Rose was quick to point at, he still had her, which, when he considered the events of the day, was the best thing in the whole universe. Even if he had to share her with that bumbling ape, Adam, it was worth it. For he had the woman he loved, the one thing above price, the one thing the Doctor needed most. He had his Rose.