Author's Note: This story contains graphic sex.

Author's note continued: In my fic of oneshots, "Ouroboros," I introduced a character named Gaia to be Mikey's friend and eventual lover. In my oneshot "Lightning Crashes" I had her give psychic comfort sex to Leo, Raph, and Don during Mike's coma, although with Don it was physical. In this oneshot, I explore and exploit the chemically-driven relationship between Gaia and Donnie, what it means to be in a polyamorous relationship between one lover and several siblings, and why it is not weird if your brother assists in your romp with his girlfriend while monitoring everything on computers. For science. You see, Donnie wound up falling in love. This was fine with Mike, as long as the proper rules were put in place. Polyamory means communication and trust.

The characters are now as spirituality and psychically close in ways that make sex nearly less exciting, on a lower level. Raph and Leo are thrilled with their psychic sex arrangements with Gaia. Gaia sports a lot of psychic sex bruises! But it's fun! It's freedom.

Now, the reason Mike and Gaia realized that Don would be better off with non-astral physical sex was because Don, like Gaia, would habitually make graphs. Lots of conversation. Maybe snacks and a movie. So much touch and sensation and power exchange.

Mike and Gaia love to push their telepathy. They adore the bizarre combinations, pushing telekinetic energy into a good sexual movement until they're floating. Imagine Donnie seeing that, his brain lighting up with experimental potential. Get in the lab now, we need to measure the fuck outta this!

An odd sort of threesome. For fun and science. This is a very open family. Gaia being part of it means having a good outsider philosophical perspective beyond canon humans or mutated humans (she is part calico). And it turns them on so hard that a messy, growling hissing threesome smashes across the lab in a telekinetic bubble. And it is nothing but fun, relaxation, and a learning experience. Donatello is gonna be sorting through data for days. Donnie didn't expect to fall in love. More stories will explore that I've had this on AO3 for a while, I think it's save to bring over to FF now.

This is literally a oneshot that sprouted from a Tumblr conversation, but it deserves its own space. In fact, this story is the beginning of Crossfire with that sex scene expanded.

Smut ahoy.

Mikey was spinning in one of the lab chairs, humming. Donatello had gotten multiple chairs, specifically so his brothers could stop perching on his desks and tables.

"What's that?" Mikey pointed, sounding highly distracted. And suddenly Don realized he had completely forgotten some vital questions for his brother.

"Mikey, you took your medicine, right?"

"Yup!"

"Including that anti-seizure tea?"

"Yup!"

"…and that chocolate high-caffeine coffee I made for you?"

"…oh. Nope. You want some?"

"Sure. Yes, please. Go. Go get some before you leave footprints on the ceiling."

Mikey didn't move. He sat ramrod straight, hands pressed against his thighs drumming, both feet tapping a rhythm. Donnie watched out of the corner of his eye, noticing the left hand moving a fraction slower, but Gaia and Rhea said it would happen, with acquired dyspraxia and hemiparesis, and Don berated himself every single day that he could not do anything, something; until that psychotherapy session last week with Gaia where where Gaia had kissed him to shut him up and told him that no one could do anything, except maybe the M'Kari psionics and Neural Mike, and maybe even those mental coping mechanisms taking on the forms of Apollo and Hecate.

The smell of coffee and hot chocolate drifted from the kitchen. Two twenty-ounce mugs floated steadily in and slid onto Don's main desk. One contained ice, which Mikey took and sipped from loudly. Donatello looked him over: No braces, no bandages, but certain muscle groups spasmed every now and then…

"Get out of that dark part of your head, Dee," Mikey said loudly, smacking his lips. "I'm not even listening and I can hear it. I bet Gaia's gonna start charging you if you keep…y'know, ruminating."

Donnie frowned. "I mean, I'm happy to update her laptop and tablet and stuff…like a barter system..."

"Plus maybe sex."

Don spluttered, coffee dribbling down his chin. "Mikey!"

A cheeky grin. "Oh, come on. I usually see her dancing all naked in your head. I mean, she can't actually move like that. But sweet fantasy, dude."

"Mikey, please just drink your coffee quietly. Your polyamorous pansexual lover is here for my psychotherapy, not more comfort sex."

Shrugging, Michelangelo downed the rest of his coffee and let out a sigh. "Fine, go work on your equations and your data. Can I check out this pile of junk over here?"

"I guess so. It's leftover Kraang technology."

"Oh, even better! I get to be Crazy Backwards King!"

"I…Mikey, with the Kraang gone, I don't think it will even work."

"Eh, you never know if Primey is hiding out. Or has some direct link."

Donnie sighed. Mike's imagination reached the most bizarre and fascinating places.

Mikey began to spin and run his chair at the pile when his T-Phone rang, singing "The Whole Of The Moon" by Mike Scott And The Waterboys. Mike used that ringtone for one person only.

"Kitten!" he crowed, phone to his ear, chair still spinning. "What's up, my love of loves?"A few minutes later, he shut off the phone and grinned at Donnie upside down. "Gaia's coming over. She found a thing she wants you to look at."

"Just a thing?"

"A technology thing. See, her palsy physical therapist – who's also an anthropologist – found it on a dig, and Gaia said she knew a guy, and of course the guy was you, so bam."

"Interesting connections." But Mike was already poking through the haphazard pile, telekinetically floating bits of metal. "Oh, I recognize this…hey, that's from when…wow, Don, how'd you get this one?"

And it continued, until there was the click of turnstiles and footsteps on the stairs, and Mike went flying out of the lab. Don followed, smiling softly, and when he saw Mikey with Gaia in his arms, nuzzling her head and neck like the most content joyful puppy in the world, he grinned.

Gaia Mako, deceivingly human, was laughing like bells, her waist-length black hair tucked behind her pointed furred ears, a v-slit cut into the back of her leggings to accommodate her calico tail, which was happily twitching. She was covering Michelangelo's head in kisses, cat-like nose twitching lightly. They were approximately the same height, and Mikey was rubbing his large hands up and down her feline curved spine like they belonged there. Gaia's cane, bright blue with silver ribbons, had fallen to the floor, and Donatello picked it up; the noise finally brought the lovers out of their enthusiastic hug and they looked at him.

"Hello, there, Donnie!" and Gaia put her arms around his waist and stood on tip-toe to kiss his cheek warmly. He blushed. Hugging her was different from hugging April; Gaia put everything into an embrace and held on tight, as though she could transfer her very energy through intense touch – well, she could, she was a very powerful telepath, but still. He found himself nuzzling her half-feline ear with its calico markings, breathing in the scent of her mocha shampoo. It was a scent that took him all the way back to when the turtles were recovering from the final battle with Shredder, when she would take their hands and send empathic waves of love and comfort, and he immediately relaxed.

She grinned widely and pressed her lips to his in a sweet, barely-there peck. "So, I have a thing I think you'll like."

Breathing in the taste of cinnamon lip gloss, he smiled. "So I heard." He led them back to the lab and locked it, noticing how Gaia held her cane lightly when Mikey had his arm around her waist.

From her large shoulder bag, Gaia pulled out a gleaming cylinder in ocean blue, rusted at the edges. There were various buttons in various shapes. "My therapist said that's not from Earth and it's mostly likely thousands of years old. He actually didn't want anyone else at the dig to see it, because the society is still reeling from the Kraang and Tricetraton invasions, and he knew that I had friends involved in the war. So." Gaia clasped her hands and twisted her fingers. She was starting to rock back and forth. Don hurried to reassure her autistic worrying. "I really, really appreciate you bringing it to me, Gaia. This is fantastic. Really." And after a few long breaths she stopped rocking, and Mikey's embrace tightened and he kissed the side of her head.

Donnie carefully placed the cylinder on one of the tables less cluttered and grabbed his sticky notes, writing out "Unknown Potential Alien Tech" – which made the other two giggle.

Don sat down on that table's chair, picking up each piece of metal and examining it, separating the ones with notes from the ones without. The giggling behind him grew louder, then longer and deeper, followed by kissing sounds and the brush of skin on skin.

"Heey," he said out loud, "if you two are going to have sex, at least get on that exam table so I can get my equipment and monitor it."There was silence, then a burst of laughter. He tuned it out. His ears faintly picked up words like "grab that blanket" and "hang on, I know how this stuff works" and "oh, someone's perky" – and the sound of a machine blipping and beeping. Frowning, Donatello whirled around to see the curve of Gaia's spine rising above a thick heavy blue blanket thrown across the exam table. Mikey's toes were visible, and from the way the blanket was undulating, they had taken him up on his suggestion.

Don sighed, grinned, and walked toward the computer monitors, which were already registering vitals, brain waves, and other responses. He kept his back to the table. "Hey, Donnie," Mikey called in a sing-song. "Mind if we try something new?"

Don felt himself nod and automatically glance at the brain wave monitor. With those two, 'something new' always meant telepathic or telekinetic bonding in interesting ways. What he wasn't expecting was the jolt and rush of power and pleasure flooding his head, then his body.

"Yeah, you might want to sit down for this," Gaia said, "It's been a while since I've done this. Will you let us?"

Donnie had managed to catch his breath, sitting heavily on a nearby chair. He spun to stare at them. They were both still, Mike's hands around Gaia's hips, Gaia's hands pressed to Mike's shoulders. "If…if this is what I think it is…" Don breathed out, "then yes."

Gaia glanced at Mike and gave a subtle nod. Mikey pushed his hips up hard – and as Gaia cried out, Donnie whimpered and clenched his teeth, feeling phantom muscles clench and damp heat surround him.

"Okay…stop…" Gaia murmured. "That's too much. It's like…double vision." Don felt her telepathy pull away and he almost whined. In his head, Gaia's voice smirked. Trust me, you'll have yours. This was a literal experiment. I'll get better.

"Are you okay, Donnie?" Mikey, always the worried one, was frowning at him even as Gaia picked up her pace in his lap, even as his pupils dilated and his muscles tightened.

Pushing out a long exhale, Don kept his knees together and managed to give a thumbs up, head down. He tuned everything out as Gaia let out a shuddering cry and Mike echoed it, a growl punctuating, and for at least two minutes his hips were snapping and thrusting and the growling was soft and the monitors were wild. Gaia clung to him, crying out again and again, and Donatello had to wonder at her endurance, what with chronic pain and spasticity.

When it was over, Gaia was curled up like a kitten and Mikey was rubbing her back and her legs over the blanket, humming something that must have been telepathically echoed and telekinetically applied, because the shaking and spasming in Gaia's muscles gradually stopped and she sighed like the world had been eased off her back.

Don watched the notes that the machines made, nodding and mouthing along with this thoughts. Low murmurs drifted past him. Mikey snorted in amusement. Something about a towel. Shuffling. Quiet giggling.

There was a gentle tap on his shoulder. He turned slowly, hands open at his sides.

"Hi!" Gaia chirped, and kissed him so hard he almost stumbled. She stepped up and pressed her warm body flush against him, on her toes, and that the hand not clutching his bicep was moving down his plastron. Don let out a sharp gasp and let his tongue be touched and his mouth examined by an eager half-feline tongue. It was stronger than last time, those times in his bedroom during those terrifying six months. Her hand slipped between his thighs to the softest part of his plastron, and nudged the soft cartilage that held his penis, the cloacal slit that had been affected by the mutation, the cloaca that was not in their tails but between their legs, at the lowest edge of the plastron that dipped between their thighs. The slit that was normally tightly closed was damp and just starting to open as his arousal increased, and her finger slipped inside until it found the head of his penis. His tail trembled.

Donnie let out a full-throated soft moan, his eyes involuntarily going to his brother's eyes, which were sparkling merrily, a wide knowing smile on his face, his arms folded loosely. Hmmm. A set-up, then? He felt her hand on his bicep massage downward, down his side, over his hip.

Gaia's finger was stroking the head of his penis carefully, and at that point Donatello didn't care where he was or who was watching. He closed his eyes and breathed heavily. Those thin fingers were drawing his erection out and up, and he dropped down into two eager hands. They wrapped around him as he throbbed. He thought he whispered "Nggh, oh god…" and opened his eyes, glancing down.

Knees bent, Gaia was smiling up at him, gentle and sweet, her thumb smoothing over the head of his penis. He shivered. She opened her mouth, and that unique tongue licked the underside of his penis until he felt dizzy. And then her mouth opened wider and Don watched his cock vanish into her mouth as her lips closed around. His head snapped up, his eyes widened, heat flashed across his lower body, and he saw Mikey leaning against the table, ankles crossed, grinning like a Chesire Cat, and then he shut his eyes and there was nothing but heat. Her mouth wrapped around him, her tongue flicked all over him, her head bobbed and her throat worked slowly. He barely registered the tiny moans and whines he was making. He barely realized he was clinging to a metal pole as though his life depended on it. He felt his head fall back. His cries deepened, and a tingling fiery storm of nerves fluttered around his pelvis. He thrust his hips shakily and opened his legs wider.

"He's close," Mikey said as if underwater.

Abruptly, Gaia's mouth left him. He whimpered. Then he felt her arms encircle his neck. His hands instinctively reached for her hips to draw her up. He felt another pair of hands and opened his eyes; Mike was propping her up, pushing her against Don. Gently, Mikey lowered Gaia onto Don's twitching erection as Don leaned back slightly. Gaia wrapped her legs around him and groaned. Smiling, Mike came to stand behind Don, supporting him as Gaia's weight pushed down on him. Donnie barely managed to thank him before Gaia thrust her hips forward and up, eyes snapping open to stare at him, and the whirlwind of pleasure caught him off-guard. All that pleasure and power rushed toward his belly and hips and he let out a long, low groan, feeling his muscles clench tightly. His brother tightened his grip on his shoulder and carapace. Gaia thrust again. And as that coiled sensation released, Don felt that built-up liquid release like a flood and he cried out, pumping his hips to the feeling of each shot pouring into Gaia's vaginal canal. He had no idea how long it lasted. But suddenly he was on the floor, gripping Gaia close, gasping as though drowning.

Mikey was sitting next to them, rubbing his shell. "Guys, that was awesome, I felt it all the way."

Don didn't have the strength to move, so he just muttered "fuck you and thank you" against Gaia's mocha-scented hair, and Mikey laughed joyfully.

Gaia laughed, the sound like bells. "Bet the data is going to be amazing on this one."

Normally, Donatello would have flushed all the way to his toes, but the cool compartmentalizing scientist rose up and clicked. Bodies were engines, brains were machines, sex was chemistry. And sex between psionics probably had never been studied before. His head began to clear. There would be notes, and graphs, and charts, and he would need them both back here in a few days to compare findings. Maybe he could seduce them with romance movies. How many films featured sex and science? Because these two brains were a cocktail of neurochemical drugs stronger than anything. And Gaia was beautifully creative and knowledgeable, and Mikey was insatiable and deviously brilliant, and Donnie was way too charmed, delighted, honored, and thrilled that his brother practically pushed them all together. He would keep it just between the three of them. It might be the greatest personal experiment he ever conducted.

It made him happy. So very happy.

When his little brother leaned on him, wrapped his arm around the cat mutant, and sighed joyfully, Donatello decided that nothing felt better than this.

He almost didn't register the towels that telekinetically floated around him.