He's always been good at running.
The stench of fire and decay is a permanent fixture these days. Those days. Whichever days are left. For a while, he clings to the memories of cool, clear, crisp, but those moments are all tied up in the people he lived them with, and that needles a twinge right between his hearts. Sometimes the ache builds in his chest and he swings back into the TARDIS, dances her closer and closer to the front lines-
But he always finds some distraction, some small and straightforward person he can help, and in this way he flits across the battleground gently, carefully, tiptoeing among the landmines. And still the smell of burning. The smell of death.
He helps persons, not people. He's not on anyone's side. He takes a fierce, frustrated pride in his isolation, until friends begin to fall (will fall; have fallen; did fall). Then the pride transmutes to a secret terror, a guilt that crowds out all other aches. Some days (whichever days are left), it's very hard to breathe. Some days, he goads the TARDIS so close to the fighting that, for a time, he's always been there, always will be there.
He finds his footing. He breathes. He runs.
He discovers another small and straightforward person. He remembers when he saw entire universes in their eyes and hearts and minds, once, when Big meant bravery and strength and cunning, and not overwhelming, stupefying fear. Now he closes out everything but her name, because names are small, names are straightfoward. Cass.
For seconds, minutes, eternities, he lets himself imagine. Watches a spark catch in her wry, nervous grin. There are whole worlds out there that have seen only shadows of the war. There are civilizations and wonders too small to be targets, but just large enough, perhaps, to swallow an entire lifetime. Or two.
Her eyes focus, sharpen. She seems him for a monster.
It's not the first time, but he decides with dizzying clarity that it will be the last. He holds his breath, tries to catch her gaze again, reaches again for the spark in her smile, and then, in desperation, stretches for the galaxies upon galaxies in her eyes, her mind, her heart. Just one glimpse would be enough, just one quick sad smile of understanding. Just one-
He dies, quickly and without fuss. Comes back as himself, for once.
It never fails, time after time after time: slowly, by inches, without even realizing, he molds himself into the person his friends need most. He's always been a blank slate.
Now he breathes slow, measured breaths, and remembers the monster in Cass's eyes. "Make me a warrior," he says. And it does hurt, but not for long.
He's always been good at running.