"Wow," is the only thing Jim can force through lips parted with awe.
The comfortable weight settled into the crook of his arm is sweet somehow, feels more natural even than sitting in the Captain's chair. He pokes an experimental finger at the swaddled form and grins when the digit is captured by a tiny hand barely able to span its width. He coos and a little voice coos back, the sound resonating through his chest.
Very carefully he brushes the jet-black thatch of fluid-damped hair on the bundle's head, sliding his touch downward to caress the vague points of two upswept ears. He taps the puffy nose in the center of the bruised face gently, watching it crinkle. He's never cried for himself, his mother, his dead father, but right now he's got an unfamiliar lump in his throat and doesn't know how to let it out.
For his son.
Spock looks tired, but hell, the boy was eight pounds and some change. Kirk feels irrational pride welling up in him and doesn't try to suppress it, gently bringing the baby closer. This is his son, now and forever, and damn it he's beautiful.
"Jim," Spock utters, and Jim's surprised Spock would say something so informal in the company of all the people gathered around them, even if they are busy fawning over his son. "Are you…pleased?"
And Jim can't do anything but throw his head back and laugh because it's either laughing or crying right now and yes, he's never been more pleased in his life. He doesn't know how to tell that to Spock but he tries.
"Hell yeah."
This seems to be a satisfactory answer to Spock, because he nods once and then his eyelids slide down over dark, exhausted eyes and Jim swears he's asleep as soon as his head falls back on the pillow. Jim doesn't know where the hell that baby came out of but when Spock wakes up Jim's going to make something with his own blood, sweat, and tears and hope it comes close to what Spock's given him.