Rose wondered, once, in the very very last days before the end she had no idea was coming, what had happened to the other one, the one with the leather jacket and the closed smile. She'd woken up in the middle of the night (or what passed for night on the TARDIS, anyway, more a matter of convenience than any actual solar phenomenon) and remembered him, for some reason, in that random way one's subconscious throws things up when it's reprocessing: remembered her first Doctor with the cropped hair and the wrinkles at the corners of his eyes from fatigue instead of laughter, and remembered he was gone. She saw flashes of him in her newnewDoctor, absolutely, the determination and the tiny little mannerisms and sometimes even the humor, those were the same, those were just the Doctor. But most of the time, almost all of the time, he was just gone. Just... gone.
The Doctor – the new Doctor, with the suits and the pain hidden away farther and differently – he had explained to her how regeneration worked, Christmas evening after dinner, while outside the windows the ash from the Sycorax ship was still falling. How Time Lords could repair themselves completely after a fatal injury, their cells reknitting into an entirely new body, and how the wild fluctuations in hormones when it happened sometimes caused personality change. "Weeeell... I say sometimes, I mean sort of always," he'd admitted when she'd pressed him, scratching the back of his head. "I was never very good at controlling it, honestly. Aaaactually, about half of my regenerations have been complete disasters. I think I came well out of this one, on the whole. What do you think?" And she'd looked him up and down cautiously, because this new body and speech were still so foreign to her then, uncanny, and it would take her a while before she could nod and laugh and jab him in the ribs in response to that question–
–but he still wasn't him. Not the man she'd met. Almost the man she'd met, but not quite. Not really.
And he never really talked about regeneration again after that Christmas, she thought that night. And she wondered how easy it really was, to lose yourself like that, to have your body, your personality, the way you reacted to things, to have all that change in a second and have everything you were be gone forever, whether you liked it or not. It's still death, she thought. Death of a kind. The man you were dies. He'd said it: he wouldn't be seeing her again, he wouldn't. The new man with the new face and the new voice and the old borrowed memories would go on new adventures with her, but her first Doctor was dead and gone, surely and permanently as if his body was lying six foor deep in the sod. And the Doctor she knew now, her Doctor, whom she loved so deeply he was a thing she never had to think about but just always there, who she gravitated around like a planet to a star because he was her world and her everything and she understood now what people meant by that because she just couldn't imagine spending her life with anyone else... someday he was going to die too, sacrifice himself for some stupid cause or other because he could never take a vacation, never ever just walk away even though the suffering and cruelty and crisises would never stop even so, and some new man was going to take his place, some man with a different face and a different costume and a different accent and way of looking at the world. Some new man who might not even know her.
And she could only pray that she would go first, so that she wouldn't have to be there to see it.
A/N: This was just going to be a really short drabble but then it got longer...
Somehow everything I touch turns into angst. I swear to god my first Doctor Who fic was going to be this completely goofy classic-Who Four/Six crossover, but that's been coming along a lot slower because I just don't write happy things that easily. Anyway, I wrote this while I was in the middle of going back and watching the first new-Who season after I'd run out of Ten and Eleven to watch. I wouldn't say Nine is my favorite Doctor ever, but I liked him a lot more than I'd thought I was going to.