I've been putting off posting this for about a week now... so, since it's five in the morning and my thoughts are a little muddled, I'm going to go ahead and give it a shot before I can quadruple-guess myself.

In case it wasn't already clear, this is a shipping fic- I know the summary is a bit ambiguous, so here's a heads up.

Donatello's friendship with one Casey Jones was measured in leaps and bounds.

They'd gone from strangers- or nearly so, since Donnie did have secondhand knowledge of Casey from April- to adversaries in a snap. The clang of a fork against pavement, the knowledge that nobody should have been where the sound originated from, it had only meant one thing: an intruder had stepped foot in the Hamato family's home. And an intruder had similar implications; it meant that the Foot had found them, that they were all in danger, that it was time to fight or go down fighting.

Casey Jones had been that enemy.

But, just as suddenly, the human boy had disappeared alongside Raphael. It could have been the end there, but it wasn't. He came back. Despite the hurdles that mutants and musophobia presented, he'd found his way back, whooping and hollering at the top of his lungs.

And then Casey had been an ally.

He had been an ally, yes, but not a friend; not someone like April, Mr. Murakami or even Mikey. They didn't even exchange two words before their personalities clashed against one another. Don was too passive- relatively speaking- and Casey too direct. In some ways, it was like having a second Raph around, but Donnie was used to Raph. He knew how to press Raph's buttons and get a good rise out of him if need be; Casey was an enigma... a meat-headed, single-minded enigma.

Of course, their shared interest in April hadn't helped matters.

That made Casey his rival.

And then the world flipped on its head again- almost literally. The ground itself led them through their competing phase into a proper friendship. Then again, when you help one another thwart the introduction of mutagen-secreting space worms into your dimension… it's hard to walk away without feeling some sort of kinship.

Just like that, Donatello and Casey were friends.

Every subsequent jump took longer to prepare, but each covered more distance than the last combined.

It was another couple of months before anything changed again. A month of experimenting with mutagen and street brawls, the Foot and the Purple Dragons, trigonometry and hockey… Until, one day, Casey propped himself up on one elbow and watched Don work over the turtle's carapace. Donnie didn't complain; it was better than having him prop his feet up on the desk and contaminate everything. Don didn't even say anything while the black haired teen hovered over his shoulder, even though Jones knew he loathed it and had to be doing it just to get a rise out of him.

"I got a question for you, Don."

Without looking up from his work, Donnie sighed, "If you want me to explain logarithms again, it's not happening. You've already hit your third strike."

Casey swept his arm off of the table and leaned in closer. "Nope, biology. And I just gotta ask- science is at stake here!"

"That's not how it works." The taller teen murmured, keenly aware that he was only saying it for his own benefit. Reluctantly, he put his work down. "Fine. What is it?"

When he turned to face Casey, though, he found the human nose-to-beak with him.

"Just wonderin'. How're you s'posed to kiss anyone with that snout'a yers?" He punctuated the question by drawing back- just a couple of centimeters, though, nothing to stop holding one's breath over- and poking at Don's beak.

The turtle flinched back, more out of surprise than anything else, and glared at him. He thought they'd gotten over this kind of romantic one-upmanship months ago.

"That's not a valid question, Casey. Mutation isn't evolution; there's no rhyme or reason to the physical traits it forms. My beak isn't for convenience or adapting to the land- it's just an arbitrary turtle feature on a humanoid form." Eyes half-lidded, he added, "Not that it's any of your business."

"Is now." Casey said, nodding proudly to himself, as though he'd said something remarkably profound.

Donnie was just about to point out how ridiculous that sounded when Casey leaned back in, tilted his head curiously, and pecked him just to the side of the mouth.

"Darn, missed." He mumbled into the green skin he'd met, "Looks like I need to work on my aim."

"Your…aim." Don echoed blankly, staring hard at Timothy's containment unit in an effort to avoid Casey's eyes. It came back to bite him in the tail, since the mutant in question was still frozen; more to the point, Tim's eyes were gazing sightlessly over the lab, right towards Don's workbench. Like they always were. That had been a bit of an oversight on his part.

The heat he could feel creeping up over his face burned hotter at the realization. What if Tim could see?

Casey didn't notice the lapse in attention, and even if he'd known the source, he probably wouldn't have cared. "Aw, don't make me say it again; star hockey player here, can't let everyone know my aim ain't perfect. And since I can't have it gettin' around, I figure you've gotta be the one to help me practice. Worked with trig, didn't it?"

"That's debatable." Donnie muttered, unable to stop himself. Then the rest of what Casey had said crashed down on him. "And don't take that as a yes! I- where did that even come from? What's gotten into you, Jones?!"

The teen stretched and leaned back in his chair, grinning widely, "You gotta know the rules'a the game before you can play the rink, stick master."

"Yeah, because we all know I want to be playing mind games with a tactless teenage thug-in-the-making rather than focusing on important matters."

Unfortunately, this didn't seem to deter- or enrage- Casey the way it would Raphael. In fact, his eyes positively lit up in response.

"Oh, we're playin' that game, huh, ultra nerd?"

At first, the turtle didn't understand the bizarre turn the conversation had taken. Had Jones really gone off the deep end? While it did explain his behavior, something just didn't seem right about that conclusion. When the series of words finally clicked, Don clenched his jaw at the challenge and crossed his arms over his plastron. While he wasn't going to let it go, he wasn't about to surrender to Casey without making the human regret it. "Better a nerd than a vexingly verbose vigilante."

"Weirdo" Casey snorted, grin slowly turning into a smirk.

Oh, that little- the turtle looked away, barely refraining from screwing his face up in what would have no doubt been an embarrassingly immature display. X, huh? Well, there were plenty of words that started with x, but not many that he could apply towards this game. Then again, who said it had to be relevant? If Casey couldn't call him on it, what was there to stop him?

"I swear, Jones, you're such a xenophobe."

The human nearly toppled his chair over, taken aback. After a moment's worth of flailing, he righted himself. The vehement reply he came up with was nothing short of spectacular, and well worth stretching the definition of a word.

"H-hey! I think I just proved that I'm not some kinda jerk who goes around blamin' guys for lookin' at other-" He came to a screeching halt when he heard Don snickering. A pink tinge settling across his face, he immediately veered away from that line of thought, "Oh, haha. Very funny you… you… yahoo."

This time, Donnie didn't even try to hide his laughter. Bolstered by the stunning success he'd experienced, he looked the brunet in the face, still smirking, and batted the ball back into the opposing court. "That's all you've got? I give you 'xenophobe' and you go with 'yahoo'? What a zero."

Casey looked like he was dangerously close to sulking. That could only be a good sign.

There was a long silence that finally resulted in a petulant:

"Avocado-face."

This particular addition was neither expected nor appreciated- a fact that was abundantly clear by the look it earned Casey.

"Okay," Don said after a moment, "Technically, I suppose that could be construed as an accurate assessment of my skin tone. But… really? Boar-head." He rolled his eyes and rested his chin on his hand, waiting for Casey's next insight.

It was a relatively long time coming- long enough that Don took it to mean Casey had given in and decided to get back to work.

"Cute." The human boy finally said, breaking the silence. Donnie looked up at him, puzzled by the sudden input. "You're cute when you're working. Did'ja know you stick your tongue out when you concentrate like that?"

The turtle didn't say anything. He just stared.

Right. How had he forgotten about that? It hadn't even been ten minutes. Really, that seemed like something that should have been weighing on his mind… and Donatello was no stranger to dwelling on things.

"Ya got game, Donnie. I never played against someone like you, but it's fun." For what felt like the umpteenth time that hour, Casey leaned forward, closer than Don was accustomed to, and held out his hand off to the side. "It's important to get a good challenge in during practice- keeps ya on your toes. Whadda ya say, partners?"

Unsure what else to do, searching for a way to buy himself time, Donnie shot a glance in Timothy's direction, almost looking to the frozen mutant for advice; then he turned back towards Casey and, subconsciously, smiled. It was a little nervous, a little unsure, but undeniably there.

For the first time that day, he didn't think. He didn't think about the history between them, what the future might entail, and he didn't even think about April.

He took Casey's proffered hand.

And then he, too, leaned forward, bumping his beak against the side of the teen's face, murmuring, "A word of advice, Casey, it's not a matter of aim. It's all in how creative you can get."

Unseen by the human, a grin crept over his features.

It was quickly stolen away when Casey took the advice to heart, twisting around to press a quick kiss to Don's mouth. Just as quickly, he drew away, looking immensely pleased with himself.

"I think that makes the score Jones: 2, Donnie: 0. Step it up, man, you gotta give me some competition here."

Donnie huffed, stubbornly turning back to his desk, and indignantly added one last, "Doofus."

Casey snorted and then he was gone, up from his chair and out of the lab in what felt like a single leap.

While Donatello wasn't entirely sure where that put his relationship with Casey Jones, he was willing to find out.