Donnie insists on cleaning him out first. "It's more hygienic," he'd said sweetly.
Mikey rolled his eyes. "And you know I could do it just fine on my lonesome, my darling pervert." Donnie huffed and dragged him to the bathroom while Mikey cackled like a loon.
Still, he has to admit that the process is easier with his big brother to help. Donnie is gentle, his movements slow and patient in a way that they almost never the rest of the time. He kisses Mikey's stomach when it starts to ache and rubs his belly when they're done, talking about what a good boy he is.
Afterwards, Mikey takes his brother's offered hand and obediently lets himself be led to the lab. It's nice, being invited into a place he usually has to barge into.  The door clicks shut, but Mikey knows that he's being sealed in with his brother instead of being shut out.
They left his gear behind before the enema, and Mikey has to admit it's kind of weird being in the lab naked. He knows his things technically don't cover that much of him, but he feels exposed, and also kind of cold. He shifts back and forth as Donnie fiddles in the back of the lab, wishing he had some nice pink stickers to put on his brother's mug.
"Got it," Donnie calls, accompanied by a loud clatter of metal. "Mikey, do you want to take a look?"
Mikey looks. And looks. And looks. And forgets completely about how cold he is, although he definitely feels a lot more bare.
It's funny how it's both so much bigger than he expected, but also weirdly simple. It's Donnie, so he expected wires and buzzers everywhere, but the machine is neat and streamlined in its great big metal glory. It glints in a way he didn't expect, like it's been freshly polished or something.
Donnie stands besides it, nervous as a date on prom night, or whatever the hell normal human couples do to freak each other out. "Do you like it?" he squeaks, back ramrod-straight and fingers tapping rapidly at his sides.
Oddly enough, it's his brother's visible anxiety that gives Mikey the courage to reach out and touch the thing, running careful fingers over the surface. He's seen enough of Donnie's material over the years to recognize his love and care, the pains he's taken to make sure it works like a charm, instantly.
Not to mention the nice, big purple dildo, which is cool and smooth under his fingers. Mikey gives it a little squeeze, relishing just how firm it feels.
He shoots his big brother a grin. "I love it, Donny dearest."
His brother's anxiety drops away immediately, replaced by his oh-so-sexy Doctor Donnie face. "Excellent." He pats the table he's hooked the machine up to. "Climb on, please. Hand and knees, legs spread."
Mikey does as he's told, although he can't help offering up a tempting little wriggle of his ass while he scrambles onto the table. Donnie huffs and gives him a smack, making Mikey squeal.
"I'll ask you to stay professional, Michelangelo," Donnie says sternly, reaching up to carefully adjust Mikey's position. "This is a very important matter."
"Aye-aye, capt--augh!" Mikey yelps as Donnie grabs the hand he'd started to lift into a salute and abruptly yanks it down by his side, strapping it in place. "What the hell?"
"Can't have you squirming around too much," Donnie chides, strapping him down so that Mikey's ass is in the air, his cheek resting on the table's padded surface. "Comfortable?"
Mikey squirms and grumbles, but finally mutters, "Yeah." Donnie may be a control freak, but at least his restraints never dig in too badly.
"Good boy," Donnie says, reaching between Mikey's legs to pat the rapidly swelling bulge of his hard-on. Mikey groans, wriggling anxiously in the restraints.
"Patience, Michelangelo," Donnie says sternly. There's a rustle of black cloth and Mikey stiffens as his brother moves to stand in front of him, a length of soft black cloth in his hands.
"A blindfold?" he asks, not sure if that weird feeling in his stomach is nerves or the desire to hump the table in excitement.
"In order to prevent any unnecessary distractions," Donnie says, in a tone of voice like it should be something obvious.
Mikey sighs. "Dude, you owe me big for this." But he obediently leans forward to let his brother wrap the blindfold around his head, the world vanishing behind a curtain of darkness.
He waits, but nothing happens. "Donnie?" he calls, straining his ears.
"In a minute; I'm just supplies." There's the sound of clattering, Donnie humming to himself, and Mikey would bet a week's worth of pizza coupons that the bastard is taking his sweet time finding the lube. He's just about to start humming the Jeopardy tune when his brother is back at his side, tracing a soothing hand up his thigh. "Now, will you relax for me?"
Mikey takes a deep breath, doing his best to calm his hyperactive mind to the best of his ability. He hears the unmistakable sound of a cap being popped up, the squirt of being shaken out of the bottle, and carefully lifts his tail in preparation. He doesn't hear Donnie move--
"Gah!" Mikey tenses as ice-cold fingers slip inside.
Donnie freezes. "Are you okay?" he asks.
"Fine. J-just a little startled." They're still relatively new to this, and Mikey was caught off guard by the sudden sensation, especially with the blindfold in the mix.
That doesn't mean he doesn't want more. Mikey grinds back onto Donnie's fingers with a soft sigh, wriggling his hips. Donnie quickly gets the message and starts wiggling back, carefully opening Mikey up with one finger, then two
The tip of his finger brushes up against something deep inside him and Mikey churrs, unable to help it. His cock spills free between his legs and Donnie lets out a low chuckle, giving it a fond tap that makes Mikey churr even louder.
"Jerk..." he moans.
Donnie leans over and gives him a kiss, finger-fucking Mikey all the while. "You know you love it," he whispers, and goddamn, Mikey does.
His brother's long, agile fingers are the best kind of hell, and Mikey's sweating by the time Donnie finally pulls away. He lets out an anxious little whine, shaking his hips, and then jumps as Donnie plants a soft kiss right over his hole.
"That's it," he whispers. "Stay ready for me, baby."
There's more shuffling around behind him, and then Mikey sucks in a breath as he feels plastic nudging at his hole. The dildo fills him up inch by torturous inch, until he swears it's almost pressing on his prostrate and has to fight not to grind further down.
It's built like the toys he's played with, but more rigid, and completely out of his control. The thought makes Mikey's thighs shake with excitement, and he really hopes he doesn't accidentally rub himself to orgasm before they've even started.
After Mikey's been completely stuffed Donnie gives him for a few seconds to adjust, muttering to himself as he carefully pokes and prods at Mikey's ass and tail. Finally, he asks, "Are you ready?"
"Born ready, dude," Mikey replies, doing his best to ignore his hammering heart.
There's the faintest click of a button, and then it begins to move.
Mikey's breath catches as the dildo pushes up and down inside him, so very gentle and so very cruel. It's a bit like being fucked by one of his brothers, but it's also so much more steady and relentless it takes his breath away.
There's something intoxicating about the way the machine doesn't respond to the way Mikey gasps and writhes at its touch. He can hear Donnie's heavy breathing, is pretty sure that his brother is on a fast track towards his own major hard-on, but the machine doesn't care. It just rocks, rocks, rocks, like the weirdest fucking lullaby ever.
Eventually his whimpers take on a note of complaint, and Donnie lets out a breathy little snicker. "Having fun, baby? Do you want me to turn it up a bit?"
"Please..." Mikey's voice is a rasp.
"Please, what?" Donnie's hand brushes over his face.
"Please...sir." He doesn't know whether it's out of defiance or desperation, but Mikey opens his mouth and laps at Donnie's fingers, relishing their taste. He takes one into his mouth and gives it a nice hard suck.
"Mmm..." Donnie lets out a low groan, and the machine clicks into a higher setting. Mikey gasps around his brother's finger as he's shoved up against them, fresh pleasure sparking through his guts. It hits his prostate again, and again, until he's heaving for air.
"So beautiful," Donnie whispers, bending down to plant a soft kiss on Mikey's shoulder. "So sweet like this, Mikey." More kisses, all over Mikey's trembling, overstimulated body, so that the faintest touches make him whimper and tremble around the dildo.
Donnie kisses him on the sensitive bridge, across his rocking shell, along his neck, up and down his arms and legs. He plants chaste little kisses along Mikey's forehead and then a big, hungry kiss on his mouth, like he's choking down Mikey's moans.
"You're perfect," Donnie whispers. "I've been dreaming about seeing you undone for so long, Michelangelo." Every syllable of Mikey's full name is spoken with reverence, like it's a holy thing. He plants another kiss on Mikey's jaw, lapping up a bit of drool that spilled from Mikey's mouth.
In the dark, every touch, from the machine or his brother, is a thousand times more. He may not be able to see, but his mind and body are pulsing with light.
And yet it's not quite enough. Mikey frantically humps back into the mission, cursing the straps in his mind as he jerks his own hips faster and rougher. 
"More?" Donnie asks, and oh, Mikey can practically see the shit-eating grin on his face.
"P-please!" He's never felt like this. Mikey's the party dude, the one who orchestrates the games and pranks, the one who lets himself be smacked around with a smile and kicks ass while cracking wise. He didn't think it was possible to be this out of control. "Please, sir--"
More, and Mikey's being shoved forward with every thrust, hard as he tries to grind down on the dildo instead. He's so lost in the haze of his own pleasure it takes a few seconds for him to register the scent of Donnie's hanging in the air, until he feels his brother's warm, heavy cock brushing gently across his face.
"You hungry, sweetheart?" Donnie asks gently. Well, he's Mikey, isn't he? He wouldn't be himself if he wasn't hungry. And Donnie sure smells good enough to eat.
He opens his mouth and lets the machine push him up against Donnie's cock, throat muscles flexing as he fights not to gag. Mikey's half out of his mind with pleasure, but he's a professional, dammit, and he pulls himself together enough to suck away like Donnie deserves.
It's such a strange contrast, between unrelenting force at one end and Donnie's pulsing warmth at the other. Mikey is splitting himself in two trying to have it all, to feel as much of the dildo shoving into him while also savoring Donnie's magnificent cock.
He lets out muffled churrs up his brother's length, knowing exactly how the vibrations will drive his brother wild. Hey, Donnie's not the only one in a wicked mood tonight.
Donnie's churring up a storm by now, and Mikey can't hear the settings changing over the noise. But he can feel the speed picking up, jerking him back and forth like a fucking rag doll. He's never been fucked like this before, rough and mean and yet so gloriously steady.
"Harder, sir," he begs, words muffled, but he thinks Donnie hears because it seems as if the pace is going even faster. Mikey's a heartbeat away from gag reflex, he's been screwed raw enough it starts to feel like a weapon hilt thrusting away inside him, and he's so turned on it almost hurts.
Hell, if this keeps up he might find himself begging Donnie to let him ride this thing until it rips him in two. Maybe that's the thought that makes him come, spurting down his legs to stain the pretty table.
Mikey wails around Donnie's cock and his brother pulls out a heartbeat before he's coming, too, bathing Mikey's face in bright heat. He gasps Mikey's name over and over again, and Mikey sputters his in return.
His fingers desperately scrabble at the table's surface and Donnie reaches out to squeeze it. They hold each other as they rock through the final shudders, squeezing so hard it hurts in the best way.
Afterwards, Mikey slumps down while the machine shudders to a halt beneath him; Donnie must have turned it off via remote control. He lies on the table, panting, the only sound the faint drip of cum spilling onto the floor.
From a distance he hears Donnie making his way back around the table, careful pulling the machine out. Mikey lets out a soft groan at the aching emptiness, but Donnie plants another kiss over his gaping entrance.
The straps are undone, he's carefully wiped down, and the mask is pulled away. The sudden hurts his eyes, though, and Mikey keeps them half-closed as Donnie picks him up and carries him to the cot at the back of the room. He settles them down, the frame creaking beneath them, and gently adjusts Mikey so he's sitting in his lap. 
"Can you look at me, angel?" Donnie asks as they settle down, and Mikey does, blinking as Donnie offers him a glass of water to drink and plants soft little kisses on his sweaty cheeks. "How are you feeling?"
Mikey takes a sip of water and mulls it over in his mind. "I feel...." he says finally. "I feel that we are going to have a lot of fun with the Destroyer of Worlds."
Donnie sighs. "Why am I not surprised that you named it?"
"What? It's a good name, dude." He gives Donnie a peck on the lips and a little smile. "Hell, maybe I'll give it a paint job. Get it nice and jazzed up for when it's your turn to go for a ride."
His brother's eyes bug out, and Mikey's laughter echoes through the lab.