A/N: I apologize in advance for the bittersweet ending. I really wanted to end on a more positive note since I love Nine so very much, but I wanted to stay as true to canon as possible, so it had to end on a goodbye ... uwu
Getting Rose back on the TARDIS took much longer than it should have - what with his body failing at a rapidly degenerating rate - but with the threat of Jack Harkness (now forever immortal and beating like a sledgehammer against his already weary time senses) at their heels, the Doctor was more eager than ever to leave Satellite Five behind and never, ever return.
As soon as they were safely back in the vortex once more, the Doctor stumbled down into a cross-legged position onto the floor grating next to where he had haphazardly lay Rose's sleeping body. His own body was exhausted to the point of collapsing, but his mind was still racing - scrambling to hold onto the memory of the golden light and the endless song of time that had been pouring through his head just a few moments ago.
There had been so much coursing through the time vortex - it made his time senses seem like child's play. But now that the vortex was gone, the Doctor found that all that he was able to retain were a few blurry images and half-remembered feelings.
He wondered if Rose would remember any of it with more specificity. Had she seen their two time streams entwined into eternity like he had? And, more importantly, how was such a future even possible in the first place?
A sudden stabbing sensation lanced through one of his kidneys and the Doctor winced painfully as his entire body threatened to crumple.
Please wake up, Rose, he begged silently, brushing his fingers against the back of her hand and desperately attempting to reach her mind with his own once more. There's so much that I need to tell you ...
It seemed that her enhanced telepathic abilities had disappeared along with the time vortex, though. The Doctor silently mourned the bright, shining moment when the two of them had been completely telepathically connected. It had felt so right to have her in his head like that. He wondered if he would ever be able to stop chasing that sensation ...
Another jolt of pain radiated up his right leg and the Doctor sprung to his feet in an attempt to loosen his cramped muscles. He spun dizzily on his heel as his sluggish blood flow deprived his brain of oxygen and made standing upright suddenly difficult.
He could feel the regeneration energy starting to build after about twenty-eight minutes. At forty-one minutes, Rose finally began to stir.
"What happened?" she asked, blinking dazedly up at the TARDIS ceiling above as she slowly came to again.
"Don't you remember?" the Doctor prodded, needing to know that her human mind had been able to retain.
It took her a moment to reply and the Doctor felt his hearts drop in his chest as he realized that she seemed to remember even less than he did.
"It's like ... there was this singing ..." she replied slowly.
He only half-listened to her hazy memories as he felt the regeneration energy continuing to burn in his veins. If he was lucky, they had three minutes remaining ...
"Rose Tyler," he mused softly, throwing her a bitterly amused smile. "I was going to take you to so many places. Barcelona - and not the city Barcelona, the planet Barcelona. You'd love it, fantastic place. They've got dogs with no noses! Imagine how many times a day you end up telling that joke, and it's still funny!"
His mindless rambling had its intended effect and she smiled at him - falling back easily into their normal rhythm of banter. Would they still have this after he changed? Would she even want to stay? There was so little time ...
The countdown was still ticking away in his head, urgently reminding him that he was absolutely wasting his last few minutes with the woman he loved ... But how to explain his species' regenerative abilities in one minute or less?
"But it's a bit dodgy, this process. You never know what you're going to end up with," he warned her solemnly.
Her easy grin was finally beginning to fade, and it disappeared altogether when a shock of regeneration energy hit him right in the gut and sent him doubling over in a flash of golden light.
"Doctor!" Rose cried in fear and concern.
But he couldn't let her touch him - no matter how much he wished that he could reach out and connect with her one last time. A wave of bitter regret rolled through him and made his hearts skip a beat as he realized that he would never get to hold her hand again or feel her fingers entwined with his in that way that brought him so much comfort and reassurance - not like this, anyway. That first kiss (and please, please don't let it be the last ...) hadn't been near enough - the Doctor still wanted more.
"Time Lords have this little trick," he explained breathlessly through gritted teeth. "It's sort of a way of cheating death."
Stupid, stupid, stupid. There was so much more that he needed to say, if only he had the time ...
"Except ... it means I'm going to change ... and I'm not going to see you again ..." And the heartbreak in her eyes when the Doctor told her that was almost enough to do him in right then and there.
Hold on, hold on, there's so much more I need to say ...
"And before I go ..."
"Don't say that!" she interrupted, the desperation in her voice echoing his own.
"Rose," he insisted solemnly, "before I go, I just want to tell you you were fantastic." The Doctor paused to take a deep breath, silently begging for her to smile and shake her head at him in that shyly dismissive way that she had. Please, if this has to be goodbye, at least let me see you smile one last time ...
"Absolutely fantastic," he went on, grinning widely in that goofy way that he knew usually lightened her mood. "And do you know what? So was I."
The countdown was getting dangerously close to zero. The Doctor felt the last few seconds as though they were happening in slow motion - the numbers ticking down before his eyes as he clung tightly to each and every single one.
Five - and finally, there was the smile that he had been looking for as Rose nodded slightly in agreement and continued to watch him with her quietly confused expression.
Four - he met her gaze and hoped that she would somehow be able to see all of the words that he could no longer say because ...
Three - the Doctor's jaw locked tight as regeneration energy swelled through every single cell in his body and he could feel himself being slowly torn apart.
Two - his mind desperately reached out and cast one last thought her way, knowing that she would never receive it with the two or three steps that remained between them ...
One - Rose Tyler, I ...
There was a sudden, fiery explosion of energy and the Doctor's eyes screwed shut against the pain as his entire body was slowly reformed. And then, just like that, it was over and the Doctor was suddenly staring at the woman he loved through new eyes ...
A/N: Thank you so, so much to everyone who has read, reviewed, followed, and/or favorited this fic! Each and every single one of you are a treasure and your kind words inspire me more than I could possibly say!
There will be a sequel to this fic following Ten and Rose's adventures in season two so stay tuned for more! If you'd like, you can also support this fic on AO3 and Wattpad, and you can follow me on Tumblr chasingthecosmos.