When Jim was ten years old, he'd clutched his pillow to his chest, got out of bed and stood outside Frank's room, listening to him snore. He'd also thought about killing him- thought about pressing that pillow over his face until there was no more breath in his lungs and he could never hurt him or Sam ever again. He'd thought about it, and thought about it, and thought about it, until the sun crept in through the window and Frank's alarm went off. Then he'd scrambled back into his room and made like he had just gotten up too.
He was of two minds about not going through with it. On the one hand, he knew that there was at least one part of him that was better than Frank. On the other hand...
"You could have ended it then," Kirk- the other one, the stronger one, or so Spock had theorized- jeered. "You could have told Sam that he was safe, instead of begging him to come home in time for Mom's call so you wouldn't 'fall down the stairs' again."
He punctuated his words with blows, until Jim was curled on the floor in the familiar fetal position, arms thrown over his head in an attempt to protect himself from an injury that could really hurt him.
"God, even now you just take it, don't you Captain?" Kirk sneered. Jim didn't bother uncurling himself for a look, but he heard the sound of a belt being unbuckled, and winced. That was going to hurt. "Just like you had us do on Tarsus."
Oh.
Oh shit.
"Don't, please-" he started. Kirk kicked him again.
"Don't beg," he ordered, disgusted, as he wound the belt around Jim's wrists. "When does that ever do any good?"
Never, but what else could he do? He had no more of a chance against Kirk than he'd had against Frank, or against Kodos' men (or Nero or Khan or the Klingons)...
It was almost reassuring, in a way, how familiar it all was: the feeling of helplessness, the pain that built and built until his throat was raw with screaming, the sickening feel of blood drying on his skin, pressing his arms over his face so the tears he couldn't prevent at least didn't show...
"You're pathetic," Kirk snapped. He was several feet away now, the sound of running water meaning that he was cleaning himself off. Jim couldn't bring himself to move. "Such a pathetic, needy bitch. No wonder you can't get anyone to stay with us."
Kirk came over to where he was, and gave him a friendly sort of slap on the side. Jim flinched; Kirk laughed. "Man, am I not going to miss the urge to do that."
He walked towards the door, pausing just before it to say "Remember: Mom can't know!" and shut the lights off on his way out.
Later, Bones tried to persuade him to let him try and stabilize the two of them as separate entities. He could do it, Bones swore, if he could just have Jim's permission for the time. But he refused, for both of them. He needed to be able to lash out every now and again, in self defense, and in the defense of other, and he... and Kirk needed to be able to remember how it felt to be the one on the receiving end of someone else's temper. Jim Kirk was both of them, fucked up and angry and frightened, and the person who grew out of a kid who once thought about killing his step father but drove his beloved car off a cliff instead.
So they both stepped on the transporter, and as Scotty energized he tried not to think about how differently his crew might look at him, those that now knew what he could be.