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Sometimes she wonders about regeneration.
Not seriously—she can't imagine who she'd be if she didn't bleach her hair like her mum taught her; if she didn't drop her r's like Mickey or bite her tongue when she grins—only… it's just that she's been through so much, in this silly human body of hers. After meeting a being named after his face, getting possessed by a face, and having her face stolen, the Doctor up and changing his own seems almost natural.
She could see how it all weighed down on him; how he'd carried his burdens in secret places—the dip between his shoulders, the grimace he tucked under his smiles. But then he traded in his leather for pinstripes got better at hiding his hurt, and she's almost envious of that kind of psychology—just evolving when the universe grows too hard for you. She does her best to keep up, but she can't escape the fact that it takes more effort for her to recover from all the running, and the face business, and… something else. Something more. Something lyric and timeless and beautiful that she can't quite remember, but still hovers, golden, in the dustier corners of her mind.
It's astonishing how quickly it all comes back, to be honest; all it takes is the sight of four Daleks emerging from the sphere, the sound of their screaming, and suddenly she remembers everything. What she did, what she saw; the lives she changed and the words she scattered. Later—after—it will feel like a blessing. Knowing what she's capable of, obstacles like dimensional retroclosure seem downright trivial.
She spends her time thinking about beginnings and endings, because thinking about the middle is excruciating—the part she'd thought they'd gotten right. She said no, and he came back for her, and they'd been fighting to stay together ever since. From the Blitz to the coronation, from the Olympics to Krop Tor… every time they got comfortable, they got ripped apart again; like a game the universe was playing.
How silly of her, to think they'd been winning.
Maybe a storm really had been coming; maybe she shouldn't have said never ever. But… they should have been safe. She swallowed Time for him and he died for her, yet somehow—impossibly—it still wasn't enough. She fell anyway.
But there are many things crueler than fate, and the Doctor is one of them. When he says you can't, it cuts even deeper than not hearing the truth he ran out of time to admit. Because how dare he decide which rules she can't break? Maybe he's ready to give up, but even the concept is foreign to her—down to her very biology. Because that's the truth about regeneration, she thinks; it's a death before it's a rebirth. Abandoning the old to make room for the new. He's allowed to say it's impossible because he won't have to live with it: in a day or a month or a year or five thousand years, he'll change again and she'll be as distant to him as the Time War and Sarah Jane Smith are now. (Another name he never mentions, another wrinkle in his brow; another companion who withered and died.) He's always called himself a coward, and maybe he should—because despite the lack of safety net, she's still jumping. Making choices and sticking to them because she has to, if she wants her indelible, ephemeral humanity to have any kind of impact at all.
And that's the heart of it, she realizes. He never understood; not even when they were at their most equal. He made sure that she'd die slowly as a human rather than live briefly as a god, and she's grateful—but for all his talk of just how extraordinary her species can be, he has no idea how much further she can bend before she breaks. The sky goes dark and she steps through worlds; the universe gives a shove, and Rose Tyler pushes right back.
Someone's got to show him it can be done.