Bones doesn't like Space. This we all know. Vulnerable!Bones and friendship or love however you choose to look at it.
How does he do it damnit?! How can he get up each day with the thrice-curst, indomitable sureness that he'll come out on top? How can he handle the pressure knowing each of his decisions could destroy them all instantly?
Leonard McCoy has known Jim Kirk for long enough to know the kid doesn't just make things up on the fly.
All of the time.
Genuinely Kirk thought out his missions and tried to plan for all possibilities. But more often than not, the world shat on the Enterprise and Jim resorted to flying by the seat of his pants and turning a tricorder into a nuclear bomb to save their asses. Leonard knew how he did that though. Jim was a genius. Clear and simple, the damned kid's brain worked about a mile a minute faster than his own, and it was always working down corridors of thought only some sick, twisted, malevolent god would use.
What Leonard didn't know however was how Jim never seemed afraid. It didn't matter whether they were warping into a hostile situation blind, or they were trying to rescue hostages from a psychotic dictator bent on torturing them for information.
Jim. Was. Never. Afraid.
He would swing into the Bridge with a goddamn green apple in his hand and commands coming out of his mouth and in ten minutes everything would be all better.
And Leonard would have a SickBay full of half dying ensigns, lieutenants, and civilians. Sometimes even enemies would be sent to him to be saved. And Jim would say to him, "You got it Bones?" and he would cuss and shout and fix them.
But it scared him.
His medical skills weren't something Leonard ever doubted, but even he wasn't a god. Or at least he hadn't paid one off like Jim seemed to have done. He had laser scalpels and tourniquets, he had hyposprays and he had dermal regenerators. He had blood pressure charts for each known species and a formula in case he encountered something new. He had a lab stocked with enough replicators to generate any vaccine and cure he needed. But he still was just a man. And sometimes everything in the world wasn't enough.
And to make it even worse, McCoy was terrified of space. Jim had told him once that he'd chosen the wrong course because 'Starfleet operates in space', or something to that tune. But Leonard had nowhere else to go. His heartless harpy of an ex-wife had left him with nothing but his bones, and goddamn her she was even responsible for Jim calling him Bones now.
But here he was, trapped in a tin can in the middle of a singularly inhospitable and unforgiving environment trying to save people's lives. Trying to not look out view ports when he walked down the corridors. Trying not to go onto the Bridge with its horrific panoramic view of nothing. Trying not to think about the hiss of airlocks and the trill of the transporter. It terrified him.
He couldn't sleep. Could barely eat. He drank coffee like an addict and popped supplement pills like candy. He stayed nearest the centre of the ship so he wouldn't get an accidental look at whatever nothingness they were currently screaming though at a speed he couldn't even grasp because there wasn't anything to judge it against. There were no trees to watch whip by and go 'oh, I'm going 50 miles per hour'. The stars and planets and galaxies they traveled past all looked the same. They were all points of burning, unwavering light that crawled past imperceptibly until they were well beyond hailing distance, disappearing in a flash and smear of light. The hum of the engines followed him all his waking moments. The fluorescent whine of the lights reminded him how fragile their ecosystem here was. A single photon torpedo aimed at the right spot would knock out their life support. What if their backups failed? What if what if what if.
It was no wonder he drank. But he couldn't even do that enough. On this damn ship he had to be ready at any time for something. And it was that something that he was afraid of. If someone soldered themselves to a cowling in the engine room, or someone scalded themselves because they tried to alter a replicator, or someone was squelched in a transporter malfunction, or if an omnipotent alien intelligence took over their body and burned up their metabolism in an effort to build android lookalikes, he had to be ready to save them. His hands couldn't shake, and his eyes couldn't be cloudy. His mind had to be sharp and his heart had to be steady.
He wasn't Jim by any stretch of the imagination. He was a surly, old, down-beaten doctor who still blamed himself for the one death he should have prevented, and couldn't hope to see his daughter more than a few days every five years. He was terrified by the very thing outside the walls of his home. He was terrified of every way onto or off of his home. He was terrified of his god damned home.
It was when two strong hands wrapped around his arms that Leonard knew he'd tuned out of the world too far. He looked up into startling baby-blue eyes and tried to smile, tried to be gruff and brush it off. But just as he knew who Jim Kirk was, Jim knew who his Bones was. Jim knew what he was worrying about, and he knew what he was agonizing over. He just shook his head after a moment and leaned his forehead against Jim's.
He was terrified all the time. But he had Jim. And he knew that Jim was scared sometimes as well, he knew that Jim worried when people didn't come back under their own power. Leonard knew that Jim kept it together at those times because he knew that he had McCoy to count on. And McCoy also knew that he had Jim to count on as well.
"But I'm still scared," he whispered.
"I've got this Bones," Kirk would murmur against his skin and hold him tight. And for a little while, sometimes just a few moments, it would be all right.