Jonatello oneshots I found on ao3

Shark attack in the aquarium

Summary:
It wasn't often Casey went nonverbal, but when he does, Donnie is there to help him!
They just wish their boyfriend would take the accommodations they made for him a little more seriously, and not repeat "shark attack in the aquarium".

Casey Jones did not go nonverbal often. If anything, he was extremely vocal when overstimulated, verbal stimming to his heart's content, or infodumping to calm himself.

But not often does not mean never, as seen by how Casey now sat in his boyfriend's lab, watching intently as they tinkered with his T-Phone. He sat wordlessly, for once, staring with those wide puppy-dog eyes as Donnie worked, head resting in his crossed-arms that leant on the top of the chair. It was midday on Thursday, meaning Casey should be in class - but it was Casey, so he wasn't. Donnie was only acutely aware of this, but didn't bring it up. There wouldn't be much point, Casey wasn't able to talk.

Scratch that, he wasn't able to talk yet, adding the last finishing touches to the AAC app they were implementing into his T-Phone. It wasn't too strenuous of a task, mostly just copying the code of the AAC app they added into their own phone. Though Donnie went semiverbal or nonverbal a lot more often than Casey did, they still cared about their boyfriend, and wanted him to be prepared if he were to go nonverbal again. They smiled to themselves when they deemed their code as complete, leaning over the desk to hand Casey back his T-Phone.

"It should be working now," Donnie spoke gently, careful of their speaking volume, "try saying something."
Casey looked back for a second more, eyes still wide. It wasn't often Donnie considered their boyfriend adorable - they considered him cute many times, but being cute was separable to being adorable in Donnie's book. Yet, seeing Casey look back at them with puppy-dog eyes and in an oversized hoodie (having changed into spare clothes he kept around the lair due to his current clothes and binder being too restricting) turned Donnie's stomach all gooey.

Other than the noises of tapping, there was quiet once Casey looked down to the T-Phone, Donnie patiently waiting. They expected him to try it out by saying a phrase pre-built into the system, such as "how are you?" or "I'm nonverbal", but did not question Casey's ways. It took a minute or so, most likely due to how he had to input each individual word, but eventually, he formed his sentence.

"Shark attack in the aquarium."

Donnie quirked up a would-be eyebrow of their mask, staring back at Casey's shit-eating grin. They pondered for a second if they somehow imputed the code wrong, but a glance at the T-Phone showed that he did, in fact, manually put in those words in that order. Before they could question what the message meant, the robotic voice spoke twice more.
"Shark attack in the aquarium. Shark attack in the aquarium."
"Case-" Donnie half-sighed, half-snickered out, taking a deep breath in an attempt to steady themselves. "I implement an augmentative and alternative communication device into your T-Phone, and this is what you do with it?"
There was a moment of quiet again, and Donnie wondered if maybe, just maybe, Casey would put something normal.
"Shark attack in the aquarium."
Wishful thinking. It was Casey.

It was Casey. Donnie couldn't help but start to laugh. It was such a stupid and ridiculous thing to use the device for, and it was such a Casey thing to do. Donnie's stupid and ridiculous boyfriend, and God did Donnie love this stupid and ridiculous boy.
"Anything else?" Donnie chuckled out, leaning their face against their hand. From the look on Casey's face, he was seriously considering what to say.
"Shark attack in the aquarium... please."
"You're my idiot," they spoke affectionately, swinging their legs underneath the desk in a way to stim. This was how they showed love, and the teen knew that.
Another quiet fell, Donnie yet again wondering if Casey would say something remotely regular, maybe even reply to their comment of him being their idiot.

"Shark attack in outer space."

It took Donnie a second to process what that meant, still not having fully processed what Casey meant by "shark attack in the aquarium" in the first place. But something clicked.
"Jones, are you referring to Armaggon?"
A nod came from Casey, repeating "shark attack in outer space" , much to the dismay of Donnie.
They sighed a little, "what have we said about joking about stressful events?"

"Shark attack in the aquarium."

"Dammit, Case," Donnie giggled out, standing from the desk, "I'm going to get us a snack, we've gone too long without eating. Do you want anything specific?"
"Shark attack in the aquarium."
"Oreo's it is," the genius hummed, moving towards the door.
"Hey, Donnie?"
The aforementioned terrapin looked back, a slight smile on their face at the fact Casey was using the device properly, "yeah?"
"I love you."
Dammit Case. Donnie could have melted then and there, their smile only growing.

"I love you too."