This is beautiful ♥ Extremely atmospheric—the clinical purity of the room, contrasting so powerfully with the chaos and destruction of the war, the Doctor's emotions and desperation, his exchange with Seren, it was all very powerfully conveyed and really chilling. The dialogue was packed full of meaning in just a few words, to the point—“Time dies.”/“And Gallifrey falls.”/“It has to end.” Beautiful. I love how he didn't want to be a hero, too, nor a warrior, only a Doctor—but the universe currently needed a warrior. And the distress signal calling insistingly from the TARDIS—calling him, apparently, to one last saving mission, but really to his destiny on Karn. That last line was a real punch, so meaningful! It's really, really striking, such a terrible moment for him and perfectly portrayed. Great job!

A few typos I glimpsed:
"A cold sliver ran down the Doctor's spine": shiver
"It's just that sometimes not of them are good ones.": none of them
"A crack splinted one white wall.": splintered
"Thunder ratted the room.": rattled