Donnie finds the card on his lab desk, tucked innocently among his files and folders. Admittedly, the bright pink color should make it fairly hard to miss, but he's still in that haze where everything shrinks down to coffee coffee coffee, his brain slowly putting itself together with each sip.
So, he doesn't really notice anything's wrong until he plops at his desk, looking down at his notes. And then--well. It's the sort of the thing that can really shock your brain to full awareness better than coffee ever could.
Mikey has given him a Valentine's card, carefully snipped out from pink construction into the shape of an open, beaming heart. It's got sprays of pretty white decorations glistening around the carefully cut edges, weighing it down slightly as Donnie picks it up.
He can see his brother's written a greeting across the top in glittering gold. His handwriting is neat and precise, the way people don't think his brother's capable of when they've never seen him in the depths of an artistic furor.
Happy Valentine's, babe, it declares. We got you a present! 
"We," being Mikey and Leo, because Leo certainly dominates this present--at least, his picture does. The shot has clearly been taken with care, so it can be printed out and cut into a fairly-well fitting heart shape, without leaving out too many important bits, before being pasted on.
So, Donnie can see all the deals. He can see the flex of Leo's thighs from where Leo's been pushed down onto his knees and stomach, bruised ass stuck temptingly into the air. He can see how tightly Leo's been bound, wrapping in so many elaborate knots it's probably a knot to defeat even his formidable skills.
And he can see Leo looking back at him, cheek to the pillow and head turned slightly so he can picture out of the card with a soft, dazed-looking blue eye. Fuck, but if all Mikey had offered with an image of that one eye, Donnie would be just as hard in his shell as he is right now. 
Of course, Mikey doesn't do anything with minimalism. For example, he's clearly put a lot of work into maintaining a good color aesthetic, matching the occasion.
For example, the ropes binding Leo are a bloody red, beautiful against the dark bruises that form when they rub against his skin. His ass has obviously been spanked long and well, turning it a rosy pink to match his fierce blush. Spots of crimson and rose blossom all over his blowers
And then there are the white accents--ropes of cum staining Leo's shell, caught in mid-drip down the back of his thighs. That fine soft tail of his has been obediently lifted to expose his hole: a perfect little knot of red, pink, and white that shines as perfectly as a peppermint.
Donnie's fingers tense at the site, scraping along the edges of the heart. The decorative lining crumbles at little of his touch, dried pieces shifting and wriggling the paper. Donnie takes a deep, slow breath and breathes in a very familiar smell.
Hmmm. Now that he's getting a better look instead of being sucked in by Mikey's photo...well, he certainly has a good idea of what his brother's cum looks like. Oh, yes, Mikey has outdone himself this year. Donnie pushes to his feet and hurries out the door.
He bumps into Raph in the hall outside and barely has time to say an automatic "Morning," before he sees the card in his brother's hand. It's red, not pink, but covered with those same familiar decorations.
"You too?" Raph asks, pointing at Donnie's card. Donnie just shoves the pink hard into his hand and snatches up the red one, looking it over as carefully as a specimen under a microscope.
This is of Leo sitting up (oh, that must be hard on his poor little ass, even with a soft bed) and facing the camera, but with a cheery pink blindfold pulled tight over his face. His head is lolling back, face flushed, drool spilling from his mouth, legs spread to reveal a vibrator buzzing away in his whole.
Cum blooms from his reddish-purple, clearly tormented cock, blossoming before Donnie's eyes like a flower. How long had it taken Mikey to get the perfect shot?
"Damn." Raph lets out a low whistle. "Little shit can get a lot done fast when he gets his mind to it, yeah." He taps his finger to the blazing little spot of Leo's photocopied ass.
"Yeah," Donnie replies, not afraid of feeling a little awe. A thought suddenly occurs to him, sending his lips curling into a smile. "He must be exhausted. Both of them."
Raph meets Donnie's grin with a devilish smirk of his own. "You know what, Dee? I bet they are."
Mikey's bedroom door is unlocked, and the two turtles inside are sleeping together, curled into a defenseless tangle. Leo stirs first, but he's still bound, a nice plastic gag shoved into his mouth, and all he can do is squirm and whimper.
"Mmm?" Mikey's eyes crack as Donnie and Raph slip inside. "Did you like your present, guys?"
"You know it, baby," Raph purrs. He crosses the room in a flash, wrenching a squeak out of Mikey as he pins their little to the bed. Leo rolls his eyes, like Donnie can't very well see his brother's tail flicking out between his bruised thighs, fluttering in anticipation.
"Now we get to give you two angels something in return," Donnie says, closing the door behind him with a soft click. Yes indeed, he thinks today will be a Valentine's to remember.