"The needs of the many outweigh the needs of the few," Spock said, and Jim knew that phrase, had heard it somewhere, and it scared him, and that's probably why he yelled, "Spock, we're talking about your life!" instead of something constructive.
He didn't think about it, later, as he composed his report. He very carefully didn't think about it.
He continued not to think about it, except that one of the many, many things Jim Kirk had always sucked at was letting sleeping dogs lie, and he dreamed.
He woke, over and over, with a memory of thick glass and a blurry shape on the other side of it—blurry because his secondary eyelids are reacting poorly to the radiation and he can't see, but he knows it's Jim, come to be with him at the last and he's absurdly grateful; it's selfish, because he can hear in Jim's voice that this hurts him, but he's grateful all the same that he will not die alone.
And Jim muttered "Or the one, or the one," to his ceiling in the dark, and tried to swallow the fear that rose in his throat.
Jim thought he could be forgiven for not making the connection sooner; the face didn't match Old Spock's memories in the least, even allowing for thirty years of aging, and he was hard-pressed to picture a Terran male who looked less like he should have been named Khan Noonien Singh than their prisoner. Jim suspected a whole lot of time under a protoplaster and some serious chromatic retagging—it wouldn't have done for Marcus's pet superman to be recognized, and at Fleet of all places there were enough people who might have seen one of the pictures that had survived the Eugenics Wars. Regardless, Jim didn't have time for the sick twist of his stomach, firmly did not have time for it on the long run for Earth, and it wasn't like the circumstances were the same. Khan didn't have a ship; Khan wasn't out for Jim's blood. If anything it was Jim who had to restrain himself, hour by hour, from going down to the brig and doing something unforgivable.
And then Scotty said that the warp core was out, that anyone who went in would die from the radiation, and Jim clamped down on the laughter because he knew that once he started he wouldn't be able to stop. Spock, at least, was on the bridge, and wouldn't leave it; Spock trusted Jim to get them power, to stop the fall. And Jim was not going to let him down. The other Kirk, the better Kirk, had let Spock do this, but Jim could beat that other man in just this one way.
Scotty wasn't expendable either; Enterprise would need him to fix her up and keep her healthy. But she didn't need a captain whose primary qualification was an overdose of what Jim's mom had always called the Teela Brown gene, so that made the decision easy. Scotty never saw the hit coming, and Jim didn't look back as the hatch closed behind him.
Fate was fucking with him. The needs of the many, Jim thought, and, Well then I'll be the one, and hit the release for the inner door.
He made it back to the main hatch mostly on force of will and didn't have anything left to pull himself into a dignified position; he ended up huddled on the floor, leaning on the wall. It wasn't until he registered movement that he realized he should close the inner door again, so that they could come in and get his body out—his body, oh God, but at least it wasn't Spock—without having to override anything.
Jim could still see, which was nice, but he didn't have the energy to look up; he groped for the door control and hit it as Spock knelt on the other side of the glass. It wasn't really glass, it was transparent aluminum and doped to within an inch of its life to resist radiation, and Jim tried to focus, because this was fate and he knew he didn't have long. Spock's hands moved, fluttering like he wanted to reach out. It was a shocking lack of control.
"How's our ship?" Jim asked, hating the sound of his own voice. It sounded almost normal, and he wanted it to sound as wrecked as he felt. At least he didn't hurt.
"Out of danger," Spock said. "You saved the crew."
"You used what he wanted against him," Jim said, trying to distract him. "That's a nice move."
"It is what you would have done," Spock said. Jim could hear the fissure opening, gaping under Spock's determination not to make this harder for him, and oh God, he knew this feeling.
"And this...this is what you would have done," he said. Maybe Spock would ask his older self, later, and find out just how literal that was. "It's only logical." It was, it was logical, but still Jim was tired, and cold, and "I'm scared, Spock. Help me not be. How do you choose not to feel?" He thought it might help, but Spock didn't respond right.
"I do not know. Right now I'm failing." Spock said, misery lacing his voice. Jim thought about making a joke, thought about saying that hating this kind of thing was why he cheated on the Kobayashi Maru, but he had things he needed to say and no time to say them.
"I wanted you to know why I couldn't let you die," he said. "Why I went back for you."
His vision was going grey-dark from the edges in, but he could still see it when a tear slipped out of Spock's eye, and Jim hated it, hated that he was the thing that could break Spock. "Because you are my friend," Spock said, and when Jim tried to agree he choked, so he fumbled a hand up onto the door. Spock's met it, fingers parted in the Vulcan salute, and Jim tried to match the gesture, tried to pretend he could feel Spock's body heat through the glass.
Tried to smile to thank Spock for being there, but the dark crept in to the center of his sight and the last thing he saw was the look on Spock's face, and Jim thought, Oh, someone's gonna get it, and then he didn't think at all.