happy turtles galore

Just a normal, plain, 'boring'—according to Leo—textbook, picked up from the library.

Later, when everything spills out into the open, April will helpfully remind him that he had, in fact, picked it up from the mystic library, and that the textbook did, in fact, have a warning etched in a rune script at the back. And Donnie will helpfully tell her to shut up before he blows up her phone with a flick of his wrist.

But that would be later. And this would be now.

‘This’ being Donnie, sitting cross-legged on the floor of his lab, music blasting loud enough to rattle the loose screws in his shelves, with the aforementioned textbook in his lap and a pencil rolling between his fingers, flipping through pages with one hand and eating Tic-Tacs with another.

Honestly, he doesn’t even know why he picked this book up. Raph had wanted to go to the mystic library to get a how-to guide for dealing with your friendly, neighborhood paper-made ninja enemy-turned-friend-turned-houseguest, and had asked Donnie to tag along. And Donnie, being the best brother ever, had agreed.

He loves the mystic library. Loves it in the way only he can—intensely, obsessively, like it’s something alive that might love him back if he stares at it long enough, surrounding himself with shelves upon shelves of knowledge written in so many languages and scripts it makes his brain itch in the best way possible. He’d dragged Raph through it like a manic tour guide, pointing out things he definitely did not care about.

“—and this section is entirely dedicated to cursed time loops, which is fascinating because—”

“Donnie.”

“—if you think about it from a nonlinear perspective—”

“Donnie.”

“—theoretically you could trap someone in a recursive—”

“Donnie.”

“—what?"

“We’re here for one book.”

"…I don't like you."

The wonder of it all had been so incredible that when the time came to leave—or more accurately, when they were forcibly removed by the stern librarian and a disturbingly coordinated swarm of bats—Donnie hadn’t managed to decide what to take home. Standing there frozen between twenty equally-appealing choices under the librarian’s increasingly murderous stare and Raph’s exhausted blinking, Donnie had done the only logical thing he could: he grabbed the biggest book within reach and shoved it forward. 

And that is how this happened.

All in all, it isn't a remarkable book. It's just big and dusty, with a worn mauve hardcover and faded gold letters saying 'The Multiverse: Missives and Mysteries' above a lined drawing of the Milky Way. Even Donnie can admit that its a wordy and cumbersome task to read it.

But hey, it's two A.M., Donnie's brain is buzzing, and he's got nothing better to do. So why not, right?

The beat drops and he taps his fingers along with it, flipping a page to read a broken-up sentence.

'—known as the uncertainty principle, which states that it is fundamentally impossible to measure both the speed and position of subatomic particles at the same time. This idea ties back into our discussion about finite and infinite measurements, as dictated by quantum physics—'

Donnie's eyes tick over to the end of line and catch an inscription in the margin, written in green ink.

'Heisenberg. Refer to page 113.'

The writing is neat and blocky, clearly written by someone who'd read the book in its entirety before Donnie had. Obediently, he turns to page 113 to find a further detailed explanation of Werner Heisenberg's uncertainty principle and the mathematical proof behind it.

Donnie reads through the familiar concepts, finding a matching inscription tying the discussion to the page he was on in the same blocky script.

Hm. Well, Donnie's never been a fan of annotated books, especially when they belong to a public library, but he does appreciate the thorough cross-referencing for his own edification. And since this person has already sullied the pages, he can't find enough guilt to stop himself from adding his own little note under the inscription—'wave-particle duality & observer effects explanation'.

A little later, he finds another similar annotation, next to a smaller paragraph.

'—so far establishing the idea that a finite set of quantum states stretches out into infinite copies in the multiverse. That's the result that many non-magical physicists struggle to attain when in reality it is quite a simple observation if one considers—'

The green ink on the side says, 'Infinite copies = infinite doppelgangers? Research further.'

Donnie hums curiously. Infinite duplications across multiverse, huh? 

Next to it, he writes, if only to humor himself, 'lmao i wish'.

Another him would be a blessing to the multiverse indeed.

Donnie keeps going, reading as much as his heavy eyes will let him, adding and responding to the mystery person’s notes in his own chicken script. It seems like the long day has finally caught up to him, because his responses get progressively more unhinged—starting with simple diagrams of arrows and atoms and turtle shells before devolving into old internet memes. At some point, he even starts writing song lyrics from a time before he was even born. Belatedly, he feels a sense of relief that he's writing in pencil instead of pen.

Under a note about Einstein's theory of relativity, Donnie hysterically writes 'dont let mikey steal the wig again', and promptly passes out on the floor.

--

When he finally wakes up, it's noon, Leo is banging on his locked door for him to come out now, brunch is ready—and directly under his latest note is a squiggle of not-so-neat green ink.

'What the shell.'

Donnie screams.

--

It takes him ten minutes to convince his family that yes, he super-duper promises that he’s a-okay.

Raph folds his arms and looks down at him quizzically. “So it was just a spider?”

Donnie sighs. “Yes, Raph-a-doodle, it was just a spider. I didn’t mean to scare all of you by screaming, I was simply startled, I am very sorry—can we please move on now and let me go eat some pancakes?”

Mikey, who’s attached to Leo’s shell like a terrified barnacle, gulps audibly. “How did a spider even get in there? Doesn’t your lab have, like, a bunch of filters in the vents? Is one going to show up in my room? Oh dear Pizza Supreme, can I please sleep with you tonight, Leo?”

“No spiders are showing up in your room, Mike,” Leo replies. His sharp eyes never leave Donnie. “Are you sure you’re okay, Dee?”

Donnie does not like lying to Leo. Not just because Leo is his twin, his second half, the pineapple to his pizza, no matter how gross the combination—but also because Donnie can almost never lie to him and get away with it. Leo always knows. Somehow.

Even now, it’s clear that he does, and just as clearly, he chooses not to push when Donnie nods, letting his expression change into something easy-going and utterly convincing. “Okay! Then first things first, hermanos—Donnie plus a brush and toothpaste. Because holy cow, your breath stinks, man.”

Donnie simply scowls, pushing past him to go to the bathroom, and mentally thanks him for letting it slide.

--

After a shower, food, and no less than two hours of frantic pacing, Donnie finally feels brave enough to write back a reply.

‘hello? is anyone there?’

Great, he thinks irritably, pouting at the page. He’s turned into the unfunny side character in a horror movie. He’s going to be the first one to die at the hands of this cursed book at the tender age of six and ten. How poetic.

He debates getting up to grab an eraser, but that would mean navigating through the several sensors and recording devices surrounding his desk that are trained onto the textbook—frankly, he’s not entirely sure there’s an opening left that wouldn’t immediately flag him as an intruder in his own lab.

Donnie sits there for an exact total of two hundred and ninety-three seconds, according to the recording on the monitor, slowly convincing himself that he’s lost his damn mind and nothing is going to happen, that he must have been the one to write that in his tired and delirious state, and who even cares what this author says about infinite realities and infinite duplicates—

—when green ink starts to appear on the page, right below his message.

With growing horror, Donnie watches a thin trickle of familiar, slow-drying green ink materialize on the paper, so mesmerized by the sheer absurdity of it that he barely remembers to zoom out and actually read the words forming in front of his eyes.

‘Hello. Yes, there is.’

Okay. Okay, okay, okay. It’s all cool. Donnie’s cool. He’s cool and fine and certainly not losing his marbles right now. There is someone inside his book talking to him. This is a totally normal occurrence that absolutely does not make him want to scream-cry-throw-up. Nuh-uh.

The recording devices and scanners prove absolutely fruitless. It seems like this book has been exhibiting no energy surges since the moment it entered his lab. Excellent. Fantastic. Love that for him.

Seeing as there haven’t been any repercussions to this whole mind-boggling event—like, for example, reality itself tearing at the seams at the clear violation of the law of conservation of matter—Donnie picks up the pencil and tries again.

‘who are you’

One eternity later, he gets an answer.

‘My name is Donatello. I am a turtle mutant from Earth. And you?’

Donnie reads that once. Reads it again. And then he screams.

--

“Another spider?” Leo asks incredulously, over the sounds of Raph trying to calm Mikey down before he dials up a human exterminator.

“Yep!” Donnie responds brightly, hiding his shaking fingers. “Another spider.”

Leo simply stares at him, disbelief etched across his face. Donnie stares right back, hoping his heartbeat isn’t as loud as it feels.

“I’m watching you, Don.” Leo says, motioning between his eyes and Donnie's with two fingers. “I’m watching you.”

Donnie just sighs and shuts the lab door in his face.

--

By the time the family interrogation ends, there’s more waiting for him, green ink sitting there like it had been there the whole time, like it hadn’t just appeared out of nowhere.

‘Are you someone interested in multiverse theory as well? I saw your notes scattered throughout the earlier chapters. You seem to know a lot about the subject.’

Donnie exhales slowly, the breath shaky.

Okay, fine. Sure. This is happening. This may be the craziest thing ever—yes, even after that one time a goat tried to take over the modern world with a few pieces of warped metal—but it is happening. He can totally handle this.

His hand still ends up a little unsteady when he writes back, the pencil pressing harder into the page than necessary.

'well i am your doppelganger, so i guess so. my name is also donatello and i am also a turtle mutant from earth, surprise'

He pauses, staring at it, chewing on the inside of his cheek for a second before adding, a little smaller this time, 'insert dramatic bow here'.

There’s a long beat. And then:

‘REALLY???’

The page explodes into smiley faces, several of them that aren't even consistent—some round and neat and some slightly lopsided, like the other guy got too excited halfway through drawing them.

‘You’re a Donatello too?? That’s amazing!!! How old are you? What turtle species do you belong to? Do you have siblings? Do you like the color purple?? Where do you live? Is it in the city sewers, because same!! Have you ever built a flying skateboard? Oh, do you have any pets? We have a cat named Klunk, he's the one who alerted me that the book was acting up tonight—’

It keeps going, the questions and observations piling onto each other into the margins like he physically cannot slow down enough to organize them, and Donnie finds himself staring at the page, his eyes getting wider and jaw dropping further.

And then, a few seconds later, right at the bottom, squeezed in next to the page number—

‘Sorry. I didn't mean to overwhelm you, I tend to get too excited. You don't have to answer anything you don't want to.'

A few more seconds later, ‘You don’t even have to respond if you don’t want to.’

Donnie doesn’t really know why that last line is the one that breaks him out of his spell, but it does. He spins the pencil once in his hand, and brings it to the paper.

'no dont apologize, i was just thinking'

Not a lie. Donnie hasn't been able to do anything except think for the last few hours.

‘i will admit tho, i dont know how comfortable i feel sharing all the details of my life’

‘That’s completely fine!’ Donatello interrupts immediately, stealing the space beneath it. ‘I understand. I am nothing but words on paper to you.’

‘but yes, i have built a flying skateboard before', he finishes, because really, what’s the point of hiding that? ‘it was for my brother mikey. i made it when i was 11. i also got grounded for it’

‘I made my brother Mikey a flying skateboard too!!!!’ The reply comes, and Donnie wheezes out a shocked sound because wow, okay, apparently he had vastly overestimated his ability to handle more earth-shattering information. ‘I haven’t gotten grounded yet. Mikey—short for Michelangelo—loves it a lot. Last night he rode it to a friend’s house just to scare him awake. It was pretty funny.’

Donnie shouldn't ask. He shouldn't ask. He shouldn't, he shouldn't, he shouldn't—

'what kind of ESCs did you use in the engines? bc when i tried it my momentum was all over the place even at half throttle'

The all-caps ‘GREAT QUESTION!!’ he gets in response is, unfortunately, worth it.

--

The multiverse theory is a strange thing.

It postulates that the observable universe is only one of countless parallel universes coexisting, each with its own variations in living beings, historical events, and even the laws of physics themselves.

Hamato 'Othello von Ryan' Donatello is probably the first person in his world to finally have proof of it, in the form of this old textbook and green ink where a different version of himself is currently explaining to him how to build a teleportation device at an increasing speed and decreasing legibility.

It’s terrifying. It’s exhilarating. It’s probably the best thing that’s ever happened to him, barring the discovery of his ninpō and the moment he found out Lou Jitsu was actually his dad.

But the wildest part of all of this is Donatello himself. The other one, that is. Because for all their similarities—which they apparently have a lot of—are just as many differences.

Where Donnie is loud, Donatello is… not quiet, exactly, but softer. Where Donnie’s confidence comes sharp and brittle, Donatello’s comes through in the ink itself, in the steady, sure lines of his handwriting. He’s still a genius, that much is obvious. But it’s different. More than anything, though, the love Donatello clearly feels for the sciences is only overshadowed by the love he feels for his family. For his three brothers, Leonardo, Raphael and Michelangelo, and his father, Splinter.

And it's all eye-opening in a way Donnie doesn't know what to do with, his fingers absentmindedly tracing the words. The multiverse theory really is a strange thing. There is a version of Donatello so much more different than this one—so much nicer and politer and kinder. A version of Donatello where someone went inside his brain and sorted everything out properly, put all the square pegs in the square holes and the circle pegs in the circle holes, adjusted the uneven edges into a package that makes sense and fits perfectly to make a uniform line of four shells.

A version where Donatello isn't a twin but he isn't a middle brother either. A version where he built a flying skateboard and it worked the first time, instead of crashing into the sewer wall at the slightest pressure and breaking Mikey’s arm.

A version where Donnie is called Donny, and somehow, it feels like that was how it was supposed to be, all along.

It's strange.

--

Leo isn't the smartest guy in the world by any means. He may not know how to machine a robot or how to punch a hole through a wall or how make the perfectly fluffy cheese soufflé, but he is fairly knowledgeable in a few areas of expertise. And those areas would pertain to his brothers.

Leo can read them all like a book. Really, they make it all too easy for him. Be it teary eyes or exaggerated pouts or Raph Chasms or maniacal laughs, his brothers are like giant walking banners announcing exactly what they're feeling at all times. Banners that are only visible to him. He's a trained pro in the art of brother-banner reading, actually.

So when Donnie, with his too-straight back and monotonous voice and shifty eyes, tells him that his lab is producing spiders out of nowhere and scaring him to death, Leo doesn't believe him one bit.

"Hmm." He says out loud to the lab door currently closed in his face. The green Do Not Disturb sign flickers on soon enough. "Hmm."

"Ohmigosh, Leo, the spiders are gonna eat me!"

"Leo, man, can I get some help over here?"

"Shit, yeah, yeah, of course."

After escorting a panicking Mikey off to April's for some girl-and-turtle bonding time, Leo's jealousy notwithstanding, Leo finds himself outside Donnie's lab doors once again. "Hmmm."

"Leo, the lab door won't open if you just keep humming at it." Raph chuckles.

"You don't know that." He replies instantly. "Hell, maybe Donnie installed a musical lock in this and the key is something only I, as his twin, would know. Hmmmmmm."

Raph goes him a look, part amused and exasperated, and leaves him be, going back to his new library book about how to deal with his buddy Frankenfoot.

His new book.

Leo looks back at the door and remembers the pencil Donnie had been violently spinning between his fingers, gaze darting back inside like he had something incredibly important to attend to.

Hm.

--

When Donnie finally leaves his lab, it's almost dinner o'clock, and this time, Leo is ready.

"Hey, Don," he says casually, lounging on the couch, "how goes the project?"

Donnie freezes right in the middle of the kitchen. "Uh. The project?"

"Yeah, the project." Leo catches the ball playing with in one hand and raises a deceptively innocent eyebrow at him. "You know, the super secret one you're working on now that's keeping you locked in your lab all day?"

It takes Donnie a second, but he takes the bait. He laughs, a short sound, his shoulders shaking a little with the motion before they sag in barely-concealed relief. "Oh, ha, I guess you caught me. My project, yeah, it's going good. Just—gathering data. That always takes the longest."

"Hm." The Donnie banner is painted neon yellow with guilt. "Well. Eat up, dude, before you jump back into it. Got your favorite today. Hawaiian."

"Eugh, disgusted grimace." Donnie heads over to the boxes, eager anyway.

"Sure, sure, you always say that, but—oh." Leo glances at the tablet on his lap. "Crap, my tablet died. Can I borrow your charger?"

Donnie shrugs, mouth full of cheesy goodness, and Leo carefully—casually—saunters towards the lab.

It's open, surprisingly. Another huge sign. Donnie never has the door open, always yelling about privacy and idiotic brothers who touch all his stuff. The free-for-all access to his computers practically reeks of wrongness.

Leo throws himself into searching through the space, looking for anything out of the ordinary. The desk is as usual cluttered beyond recognition, full of blueprints and plastic juice bottles and tools. There’s an EDM playlist paused on the monitor, and none of the projectors are running anything.

He turns slowly, taking in the space like he’s mapping it out, searching for something—anything—that feels off, when his foot bumps into something on the floor.

A pencil. 

Leo crouches, following the angle it rolled from, and finds a giant textbook tucked into the shadow of the desk footwell, half-hidden against the backboard. Ha. Sneaky, sneaky, but not sneaky enough.

He grabs it, plops down cross-legged on the floor, and flips it open.

And he screams.

Almost.

He only barely manages to stop himself, shoving his fist into his teeth with such force, his head nearly snaps backwards. Ow, that hurt.

Unfortunately, even his watering eyes can't hide whatever this is from him.

The text of the book is enough assault on his brain. It's small and cramped and trying to read it on a good day would give him a headache. But the messages on his side, graphite and the ink together crowded in the margins around the printed text is far, far worse. Leo can recognize Donnie's handwriting, could recreate it in his sleep, but the other handwriting is… just that. Other. And decidedly not from anyone in this realm.

Oh, Lou Jistu's sweet pompadour—what the hell is going on?

He gets his answer soon enough, shamelessly reading through the messages and feeling his stomach drop with each mention of a 'my Leo' and a 'my Raph', some head-spinning science-y concepts about the fourth dimension, machines that both fly and cause broken limbs and—yeah, okay, Leo might be getting a little nauseous now.

Leo lets go of the book, hearing it plop down on the floor as he tries to stare at the LED strip on the ceiling and breathe normally.

So this is what Donnie has been hiding. A haunted book where he's hallucinating an extremely physics-based conversation with another version of himself.

This is definitely not what Leo has been expecting.

"Leo? Where'd you go?" Raph's voice calls, and Leo jumps to a stand like a stringed marionette. "We were gonna watch a JJ movie."

"I vote for Pluto—"

"Not Pluto Vacation IV."

"You never let me shine."

"Uh, yeah, just a minute!" Leo calls back, wincing at the voice crack.

He looks back down at the book, grabs the first pen he can find—blue, of course—and flips all the way to the last page, past the long references and acknowledgments, to a clean, empty sheet. And he writes.

'okay, idk who you are'

…Immediately a bad start. Think, Leo.

'okay, idk who you are'

'okay i KNOW who you CLAIM to be but but idgaf atm. weve had more than enough bullshit to deal with recently and i refuse to let my brother get sucked into ur wily green charms. stop talking to him before i take this book and shove it so deep into a paper shredder even the foot clan wont be able to resurrect you. you have been warned.'

And then he puts the book back into place, leaves the lab exactly how it was, and saunters out, cool as a cucumber.

--

Donnie wakes up with his face smushed against something broad and solid, and startles upright with a sharp inhale, sniffling slightly as his heart kicks into overdrive. He always wakes up like this—worried, anxious, his pulse loud enough to be heard in his ears.

Immediately, a large hand comes to his shell—his bare shell—and presses there, steady and grounding. “Easy, Don, you’re good. Mornin’. You’re on the couch after movie night. It’s a little after five a.m.”

Donnie rubs his eyes and blinks up at Raph, who's smiling at him gently, the curve of his mouth still sleep-tired. He must've stayed with him all night out here.

"Sorry." He says, voice gravelly.

"Shh." Raph pats him again, and nods to the other end of the couch. Leo's curled on his side, legs up to his chest and wrist bent at an uncomfortable angle that he'll probably spend the whole day complaining about. "We all passed out halfway through the movie. Pops turned it off for us. Wanna sleep a little more? I think you need it."

Donnie thinks about it, mentally cataloguing the heaviness of his limbs and the still-hammering beat of his heart. To be honest, he would love nothing more than to flop directly onto Leo's shell and conk out for a few more hours. But there is something else sitting at the front of his mind, loud and impossible to ignore.

"I think I'm gonna go back to my lab, actually." He admits. Raph nods, like he'd been expecting it. He opens his mouth, but Donnie cuts him off. "And yes, I'll brush my teeth before I do, I promise."

Raph huffs, mumbling something about 'you said that last time too' before letting his head fall back on the couch cushion and going back to sleep. Donnie shakes his head at him with barely suppressed fondness, reaches out to straighten Leo's poor wrist, and leaves quietly.

Thankfully, everything is still the same in his lab, the book standing just where he'd left it. He can't help but let out a relieved sigh. He sits on the floor and flips to the last page he'd been on with Donny, eyes skimming over the now-familiar mix of green ink and graphite.

He grabs his pencil, taps it once against the margin, and then writes.

'hey. i tried your suggestion about the energy output and my simulation works a lot smoother. thanks a lot'

And, a second later, 'im open to ideas for how to hide this from mikey before his bday btw, im gonna need them'

Donnie leans back against the wall of his desk, spinning the pencil between his fingers, and waits.

--

He keeps waiting.

Donnie isn’t a particularly patient person by nature. It’s part of his charm, really, of being one of the younger brothers—and Papa’s favorite—that he simply wishes for something and it just gets dropped into his lap. Or, occasionally, unceremoniously shoved into his face while Raph grumbles under his breath. Either works for him.

So while patience may be a virtue, it certainly isn’t one of his. Which means that when the digital clock on his wall ticks over from twelve to one, to two, and then keeps going all the way to five p.m., he feels entirely justified in the steady climb of his irritation.

He gets it, okay? There's probably, like, timezone differences or something across dimensions. Or maybe Donny just got caught up in another scuffle along with his brothers—Pizza Supreme knows how many times that's happened to him too.

Or—or maybe the magic of The Multiverse: Missives and Mysteries ran out, and Donnie lost all contact with him.

He swallows, pushing that thought down. He goes back to the page anyway, tracing over the graphite letters, and writes, 'did the connection break? are you still there?’

By the time dinner comes around again, he figures out his answer.

--

In the span of the next day, Donnie gets a lot done. Objectively speaking.

If anyone were to walk into his lab and take a look around, they’d see updated schematics neatly stacked across his desk, a partially rebuilt prototype sitting off to the side, and a brand new simulation coded from scratch running smoother than it ever has before.

They'd think he's been productive. And he has, sure. Technically.

Technically, he refines the energy output for the skateboard again, smooths out the inconsistencies at lower speeds. Technically, he reroutes half the internal wiring because the original layout was, in hindsight, deeply embarrassing, and technically, he even starts designing a new casing that won’t immediately fall apart the second Mikey inevitably uses it incorrectly.

Technically, he's been doing great. He just doesn't remember doing most of it.

Because every few minutes, without fail, his attention drifts back to the same place. To the book, kept right within his line of sight, waiting. Or not waiting, that's the whole problem.

He glances at it anyway, over and over again. Until even he gets annoyed with himself and flips it closed, shoving it into the cupboard a little harder than necessary.

When that doesn't prove enough either, he decides more complicated measures are necessary.

--

"Dang, Donnie," April says, her eyes widening behind her glasses, "did you reinvent your entire lab in this last week?"

"'Reinvent'? No." Donnie replies, spinning in his chair. "'Redesign? Yes. Lo and behold, my dear April, I present to you my new and improved lab two point oh. AKA, the lab of your dreams."

"Dee, if there's anyone in this room that dreams about laboratories, I don't think it's me." April responds, reaching up on her tippie-toes to poke at a long rope stretching across the room. "Laundry line?"

"Zipline, actually." Donnie claps twice, and the small bot on the other end of the rope rolls over quickly and drops a pack of Cheez-Its on her head. "Voila."

"How convenient." April deadpans. She peers at him closely. "Are you doing good, dude?"

Donnie turns his gaze away from her, foot tapping on the floor. "But of course."

"You sure?" April asks again. "You've been, like, weirdly closed in for the last couple of days."

Donnie stops tapping, lips twisting a little in thought, and continues. He opens his mouth once like he’s about to say something else entirely, make a joke or something, but suddenly aborts midway to say, "Do you ever think about the multiverse?"

“Yeah." April says, a little thrown but going with the flow; she's probably used to the several directions conversations with Donnie usually take. "I mean—as much as the next person, anyway. We learned about it in physics lecture a couple of weeks ago. Double-slit experiment, many-worlds interpretation, all that.”

Donnie nods slowly, feeling intensely aware of the presence of the mauve book tucked away in the cupboard he had, intentionally, rearranged to sit on his left instead of his right.

“The many-worlds interpretation.” He says, almost absently. “The theory that all possible outcomes of a quantum event coexist in a vast, branching multiverse.”

“Sure?"

"Ever think about the possible outcome of a different April O'Neil?" He asks lightly.

April stays silent. Donnie can almost sense the imprint of her stare physically pressing into the side of his face.

"Aw, Dee," she begins in a sugar-sweet condescending tone, and he automatically scrunches his nose, "are you telling me you don't like this outcome? Your favorite big sister? After everything that I've done for you?"

Donnie wishes his face would cooperate enough for him to roll his eyes dramatically like how he should at the teasing banter. "No, no. Just—never mind. Forget I asked."

He quickly clicks open his browser window again, which conveniently opens up to his last research article about quantum physics. April steps closer, close enough for him to feel her body heat. He braces for a reaction at the screen display. He doesn't get one.

"Sometimes I do, though, yeah." She answers then, unexpectedly. He blinks and turns towards her. Her face is serene, nothing but true O'Neil honesty. "Doesn't everyone? Think about a different version of themselves? Like, hey, maybe there's a version of me out there in all the star-soup that can actually hold a job down for longer than two weeks."

"One week." Donnie corrects without thinking. A smile cracks on her face. "But don't you get sad?"

"Sad that she'd be employed?"

"Sad that you aren't."

"I think my mom is more sad than I am, about that." April jokes. "I tend to spend a concerning amount of my uni fund on clothes and pizza."

"But," he helplessly waves a hand, "that could be you, though. That version of you that's working and happy. That has a uni fund and enough pizza to last a lifetime."

"Well, sure." April says without missing a beat. "But it isn't."

"Hell, there's probably a version of you out there that doesn't even have to deal with mutant turtles and all the shit that comes with them." Donnie blurts out with a humorless laugh. "Doesn't that make you jealous?"

Another silence. Her face loses the wry amusement.

"Let's be honest, your pizza money is mostly used on us, isn't it? That and first aid kits and pain meds from all our fights."

"Donnie—"

"Imagine it, April." Donnie continues, unable to stop himself. "A universe where you're a regular high schooler. No random enemies in your homeroom, no ruined school dances because a magician decided to make the building disappear. Perfect attendance and good grades and everything. And a universe where you’re absolutely getting a virus on your phone every other week without Donnie Blockers to block your searches."

There's a feeling spreading under Donnie's ribs, and he only belatedly realizes it's a bad emotion until he glances from the corner of his eye and meets the blank look April gives him, frozen in the way she gets when she's truly taken aback by something.

Oh. 

Donnie clears his throat, x-ing out of the window and pulling up a game of solitaire blindly. "Anyway. Interesting to think about, right?"

He plays without really seeing the cards, clearing his draw pile and not registering a single move and starting again. April doesn’t say anything for a long moment, which is so much worse than her saying the wrong thing, because April is loud by default and her silences are so much scarier.

And then he feels a gentle hand settle on his arm.

"Dee." Her voice isn't too soft or loud. Just plain, no emotion attached to the words. "Your brain has been doing a lot of thinking recently, huh?"

"That's what brains are built for." He replies on autopilot. "Don't let Leo convince you otherwise."

April raises a brow at him. He deflates, cowering under her gaze. "…Okay, fine. Maybe it has, yeah."

"Yeah." She repeats. "Been thinking a lot about stupid theories, clearly."

"Those theories aren't stupid, they're proven by some of the best scientists in the entire world—"

"No, but the gray mush inside this giant forehead tends to be a bit stupid sometimes." April counters, poking him in the middle of his forehead, right where his Raph Chasm would be. He scowls at her. "Why else would it be thinking about a life where I have to exist without my turtle buddies, hm?"

He shrugs, finally giving into the urge to look over to the cupboard again. The textbook lies there innocently, containing hours and hours worth of conversations nestled in small margins before the inevitable end that Donnie is still hoping against hope isn't permanent.

"Doesn't the idea make you upset though?" He insists. "That that's not you? That you could have it all better? Be better?"

"It does make me upset." April says with a firm look. “It makes me upset that you’d even entertain the idea that I wouldn’t want to be here—with you four, like this—in every universe. And if the multiverse or many-worlds or whatever theory any of those weird scientists talk about is real, then I feel upset for that poor April O’Neil out there who doesn’t get to have you with her.”

The bad emotion in Donnie's chest churns.

"And, also," she adds, "I mean this with all the indignation possible when I say that I don't have to be 'better'. I am just as good as I'm supposed to be, this way."

He gulps, guilty and caught out.

April bends a little, trying to make eye-contact. "You don't think so?"

"No, I do." He says immediately. "You're the bestest. Sorry I said anything."

She sighs, and reaches to pat him on the head gently. And, because she's April, and she's always known him better than even he knows himself, she says, "The same goes for you, by the way."

Donnie glances towards her. She doesn't flinch away.

"You can't possibly think that." He says, voice a little raw. The weight of the pencil in his other hand seems to get heavier by the second. "You can't make that assumption—you only have one data point. You need to randomly sample from a population, conduct research, run tests to get a significant result—"

"The only significant result I care about," she cuts him off, the glint in her eye both fierce and caring at the exact same time, "is what the people in my universe think of themselves. What the Donatello sitting in front of me thinks of himself. And he better know that he's the bestest out of all of them. I don't care about any other 'data points'."

"…That's not how statistics works." He argues feebly. "Or how science works."

"Count the number of fucks I give, Dee." April retorts, and it makes a strained laugh bubble out of his throat despite himself.

He rubs his eyes with the heels of his palms, feeling them burn. A loaded sigh escapes between his teeth. The bad emotion doesn't go away completely, but it stops making him feel like he'll combust under its weight. He wonders how long its been building for.

“Yeah, okay,” he mumbles eventually, “noted. April O’Neil rejects the scientific method. I’ll make sure to publish that immediately.”

“Oh, please do,” April shoots back, completely unimpressed. “I’m sure the entire academic community will be devastated. I’m kind of a big deal.”

Donnie scoffs, and lets her pull him into a hug with the back of his neck, nestling his head into the crook above her shoulder. The familiar smell of lilies soothes him immediately. For once, he doesn't feel the need to glance over to the cupboard, towards the book.

--

But, of course, not all things can be avoided forever.

To his credit, Donnie manages to make it a whole four hours before he checks the textbook again. Not like he had a choice, actually—April had practically dragged him to her apartment to do their nails together while watching old cooking show reruns. She'd even grabbed two slices of bread and called him an 'idiot sandwich' when Gordon Ramsey did it on the screen, to which Donnie'd responded by smudging her nail paint over her pajamas.

And now he's here, back at his lab again, sitting on the floor with the book and opening it one last time before the library return date approaches tomorrow. He feels an odd sense of grief at the companionship he'd gained and lost in the span of three days.

Which is stupid, obviously. Because come on, what is there to grieve? A pen pal? A magic book glitch? He has lost many things in his life. His first titanium screwdriver, his dignity after the Purple Dragons incident with that video game, that time he drew the most perfect set of eyebrows before realizing Mikey had put invisible ink in the makeup pen. Not to mention his old home in the sewers, the one he grew up in. This should really not rank high on that list.

And yet, Donnie finds himself taking pictures, carefully making sure every cramped margin and overlapping note in the book is visible. He gets everything, from all the engineering talk to their arguments about the difference between mystics, magic and ninpō, and their long-winded theories delving into the concept of the self and what made a Donatello a Donatello. He gets the page where Donnie had asked if all versions of Raphael were 'such utter softies all the time,' and Donny had written back, with feeling, 'ABSOLUTELY yes'. He even gets the page where Donny had drawn two tiny turtles in the margin, next to a diagram of a microscope and labeled it 'scientists at work'. Donnie looks at that one for longer than necessary.

He flips to the last page a little too harshly, already mentally composing some kind of closing note that is normal and appropriately casual and not at all emotional. And he freezes.

Beneath his last message, written in green ink that looks darker than usual against the paper, are two words.

'I'm sorry'

Donnie stares. His first thought is not a thought so much as a loud, static-filled beep. His second thought is more of a question mark.

The textbook seems to warm a little as more ink appears beneath it. ‘I didn’t mean to upset anyone'

Donnie grabs the pencil so hard it creaks between his fingers, and writes directly underneath the apology before he can think better of it. ‘what the hell does that mean’

For one second, nothing happens. Then, ‘You’re there?’

Donnie lets out a sharp laugh, so sudden and breathless with something like relief. ‘yes?? obviously?? where have YOU been??

The reply comes a little slower this time. 'I figured I was overstepping. I didn't want to leave you high and dry but I didn't want to make anyone worry, especially when cross-universal phenomena are involved. After what was written, I thought ending this was probably for the best.'

Donnie stares even harder.

'after WHAT was written'

A long pause.

'The warning on the back of the book?'

Donnie flips the book shut so fast the pages snap together loudly, his fingers clumsy and nearly tearing something.

And then he finds a mess of blue ink marring an empty page.

--

Leo's on his bed in his room, fiddling with a Rubik's cube and listening to music playing from his phone, when his door bursts open so hard it rattles against the subway wall.

Donnie stands in the doorway, a book clenched in one hand and a thunderous scowl carved across his face.

For one long, silent second, they stare at each other. Leo’s eyes drop to the textbook, then back to Donnie, then back to the book. The Donnie banner is nearly on fire with violet rage. 

Oh, shit.

--

In Donnie’s defense, he’d thought it was just a textbook.

It turns out to be a tool for the unimaginable. It turns out to be a bridge between one universe and another, between one Donatello and another Donatello, between one family of four mutant turtles raised by a rat in the sewers and another family of four mutant turtles raised by a rat in the sewers. It also turns out to be the reason Leo ends up locked out of Donnie’s lab until the heat death of the Solar System.

Mikey finds out because he hears the two screaming at each other, because of course he does. There was never going to be a world where Mikey heard Donnie shout, "You nearly lost me my interdimensional scientist, you banana-striped idiot," and didn’t come sprinting down the hall, multiverse theory be damned. His first reaction is understandably, fear. His second reaction is betrayal, because how dare Donnie keep the opportunity of making new friendship bracelets from him, the audacity.

Raph finds out when Mikey tells him, because of course Mikey tells him. There was never going to be a world where Mikey learned about another entire universe full of alternate turtle brothers and didn’t immediately grab Raph by the arm with enough panic-strength to leave finger marks. Donnie would say Raph takes it surprisingly well—if 'taking it well' meant sighing loudly and dropping his head in his hands, asking, "There's more of you three?"

April finds out by—actually, no one knows how April finds out. She just appears at the lair at the right time to watch Leo trying to make a flavorless cake as an apology while Mikey interrogates Donnie like a detective. 'Big sister intuition,' she explains later, but right now, she just pats Raph on the head comfortingly with one hand and throws cushions at Donnie with another, cursing him out for keeping her out of the loop.

And when Papa finds out—well. He just can't stop laughing.

Honestly. There could not have been a worse possible way for the secret to come out.

--

When the time comes to officially introduce the family, Donny responds with a careful, polite greeting. Despite their earlier bravado, everyone gets really quiet about the whole magical-ink-materializing-out-of-nowhere thing, until Mikey grabs an orange gel pen and asks Donny if his Mikey likes pizza, which is as good of an icebreaker as any.

Leo, still a little bitter, adds an apology in blue ink, and Donny forgives him so quickly and earnestly that makes him feels worse. Deserved, in Donnie's opinion.

Once Donny's own brothers get involved, it only descends into further chaos. And the book ends up becoming less of a secret and more of a family activity, in the same terrible way movie nights are family activities— meaning that everyone argues constantly, someone inevitably spills something in the middle of the page, Leo makes commentary no one asked for, and Papa ends up having to put his foot down at least seven times and is ignored all seven times.

"Ooh," April finally says, a teasing glint in her eye, "guys, I think we're embarrassing Don-Don in front of his new friends."

Donnie makes a strangled sound. “They are not my friends.”

Right on cue, green ink curls across a margin for them all to see. 'All jokes aside, I have to say—I'm really glad we found each other, Donnie'

Mikey coos loudly at the same time that Papa sniffles, emotional. Donnie just groans, hiding the flush across his face.

--

"No," is the first thing that comes out of Draxum's mouth, as he shakes his head in a mixture of both shock and exasperation, "no, no—even you cannot be stupid enough to discover an active interdimensional conduit and then keep it for days."

"C'mon, goat man," Leo jokes, "we've done stupider things."

"You've done stupider things." Donnie points out. Leo nods in agreement.

“Not the point,” Draxum snaps, eyes still fixed on the book like it might spontaneously combust. "How long has it been here, in your home? And how long until you get rid of it?"

"He was supposed to return the book yesterday." Raph pipes up, sitting on the floor playing Jenga with Frankenfoot.

"So this is a stolen interdimensional conduit." Draxum deadpans. 

"Like that was a stolen set of cursed armor?" Donnie backfires. Mikey 'oohs' in the background as Draxum's nostrils flare.

Eventually, after all the pacing and glaring and deeply unnecessary comparisons between Donnie and a toddler playing with a cursed blade—Draxum sighs.

“I have some texts, in my old lab." He admits finally. “Older than the Hidden City library, older than most surviving yokai records, about cross-universal travel that has been done successfully."

Donnie’s head snaps up, surprised. Hope balloons in his chest, large and joyful. Draxum gives him a flat look. “Don't look so excited. This is not permission to be stupid with more resources.”

“It sounds like permission to be brilliant with more resources.”

“It is not.”

“It kind of is.”

“It is not.”

But it must be, at least a little, because three hours later, they finds themselves covered in poor disguises standing in front of the old dilapidated laboratory with Draxum, the old mauve textbook tucked firmly under Donnie's arm. Draxum gives them a lecture about caution, restraint, discipline, and not touching anything unless explicitly instructed, and Raph and Leo mime him mockingly behind his back while Mikey tries not to laugh.

The textbook warms a little at his side.

Donnie flips it open all the way to the last page. All the hundreds of pages of empty margin space had finally been covered up with multi-colored inked messages, save for a small corner towards the edge, where one last sentence appears in green blocky handwriting.

'Ready to say hello?'

Donnie smiles, pulling out his pencil.

'yeah', he writes, smiling quietly, 'see you soon'.