Casey's a lot of things, but he ain't stupid. And the turtles aren't exactly hard to figure out.
Leo's the boss. Donny's the genius. Raph's the brute force. Mikey's the wild card.
You don't argue Leo's lead if you're hoping to have any of his brothers' support; you don't put down Donny's techno mumbo-jumbo if you don't want him to make you look like an idiot in three seconds or less; you don't goad Raph into a fight unless you're really lookin' for some new bruises and a few loose teeth; and you don't try to predict Mike, ever.
But underneath all that- under the masks and the secret, vigilante ninja stuff- they're kids, and Casey's age, with quirks and pet peeves and favorite episodes of stupid daytime T.V. shows, and they're brothers. They fight like assholes and they play dirty and they get on each other's last nerve as often as they can, and any given second of any given day they would die for each other, and that's a knowledge they carry quietly, like it's nothing special.
Casey picked it up after knowing them less than a week. There's protective, then there's the Hamatos. And if he was gonna hang with Raph, if he was gonna have anything to do with him or his brothers or their late night vigilante show, then he had to get behind those unspoken family rules a hundred and ten percent.
Which is why he's in the position that he's in now, meeting that skeletal werewolf-looking dude glare for glare, ignoring the razor claws and teeth and shifting another step or two to cover Mike, who landed too hard when the wolf creep threw him and hasn't found his feet yet.
Mike's his best friend's baby brother. That kinda puts the kid on a bit of a pedestal as far as Casey's concerned. Granted, he's made of the same tough stuff his brothers are, and he could hand Casey his butt on a silver platter about as easily as they could- and he's always everywhere, loud and larger than life and a walking antonym for the word 'ninja', it usually makes more sense to push him into a puddle than it does to baby him or handle him with little kid gloves-
But at the end of the day, it goes without saying. It's something Raph's never explained to him, something Leo and Don have never said out loud, it's just... obvious. Casey's got a little sister at home- he gets it.
Casey calls the question over his shoulder, 'cause he's not taking his eyes off Rahzar for a second. He can hear Mikey pulling himself to his feet. Even though it doesn't take long by normal-person standards, ninja standards are worlds different, and worry's taking front seat in Casey's brain at this point cause the kid hasn't even answered him yet.
"Hey, Mike, you with me?"
"Yyyeah," the turtle finally replies, drawing the answer out slowly like he isn't entirely sure it's the right one. "Yeah, I'm okay." There's a rattle of chains, and Mike moves up to Casey's side.
The others are fighting that fish guy and about three dozen of those stupid robo-ninjas, out of sight but close enough Casey can hear them clearly. They're like ten stories under Manhattan, whole miles from the lair, and Casey can't even remember how they got ambushed, just that Don had some bright idea about maps and security systems, and his brothers- and Casey- got caught up in his enthusiasm and tagged along. The light tower Don rigged is the only source of light in the underground, since the turtles ditched their flashlights and electric lamps the second a fight was on. Casey's gotta stick by the tower, and it's the biggest disadvantage in a ninja fight that he can think of. Mikey must be on the same page, because he stands by Casey's side instead of capering off to join his brothers, and he searches the dark with narrow eyes.
"Somethin' feels weird," he says at length, and Casey tightens his grip on his baseball bat. Those words outta Mike's mouth never bode well. "Dude, I think we should- "
With a guttural roar, Rahzar's practically on top them out of thin air, and Casey goes down, hard. The concrete scrapes roughly against his mask, and he tries not to swear. The hand that shoved him is still pressed to his back, three-fingered and next to human and distinctly unclawed. "What gives, man?" Mike doesn't have an answer, just pushes him down a little harder and talks over his head.
"Rad-Brad got an upgrade! Since when are you packin' heat, dude?"
"Oh, don't worry, little turtle. They're only tranquilizers. My master wants you alive."
Mike whistles. "That's pretty generous. Maybe he's not such a bad guy after all."
Now that Casey's gotten pretty personal with the ground, he's startled and dismayed to find it's not very... stable. "Uh, Mike- "
He's cut off as he's rolled to one side, none too gently, and Mike's nunchucks are a blur Casey doesn't even need to see. The tranq gun discharges once, twice, three times, but Casey doesn't feel the sting of a needle anywhere- he does feel the concrete under his hands start to shift with the weight Rahzar's throwing around, and his heart jumps to his throat. In about two seconds, they are so screwed.
Pounding feet in the tunnel behind them, and Raph's yelling their names. "He's got tranqs," Casey shouts back before anything else, and he sees his friend's eyes narrow, two bright pinpricks of poison green. They get trained for this kind of thing back home, with toy arrows and blindfolds, and Raph doesn't slow down for a second. Behind him, in the glare of the floodlight, Casey can just make out Donny and Leo behind him, rushing over, and Casey has a second to think Okay maybe this will be okay and then-
He's falling through the crappy floor as it rips open under him like paper- and he's panicking a little as he scrabbles for a handhold that isn't crumbling concrete. They're underground already, where else is there to fall?
The light topples over, the fluorescent bulbs popping like gunshots, and his friends are shouting at the same time. Oh, god, Casey hopes they're on solid ground. And Mike! Mike was right next to him, where is-
"Gotcha," the kid says, and two hands wrap around Casey's wrists. It won't somehow save him- too late in the game for that, Casey's learned that when you fight with physics you always lose- but those hands are strong and unbreakable anyway, and Mike's voice is almost breezy; like whatever's about to happen is all part of the plan, like everything's gonna be just fine.
And when Casey falls, his best friend's baby brother falls with him.