The Halloween Apocalypse
"Yaz, I'm fine." The Doctor says. She's lying. She hasn't been fine since Gallifrey—
Which she doesn't think about. And Yaz knows her too well.
"Don't lie to me. Aren't we friends?"
The Doctor laughs. "Of course we are."
"Then open up to me!"
But she doesn't open up. Not anymore. Twelve's unwilling regeneration hadn't made sense to Thirteen at the time, but that was when she was fresh and new and certain that the universe would be different, that he would be different, now that he was a she.
But it wasn't, and she wasn't, and on dark days, she wonders if she will ever be different again. The same old story, acted out over centuries. Friends lost, battles fought and battles won, all for her to do it all over again, incarnation after incarnation. The last of the time lords-but maybe she isn't even that any more.