Thread by @murcielagoAO3

#miyacest star//trek AU mild nsfw, switches

Captain Atsumu and First Officer Osamu command a Federation science vessel on expedition through an unexplored quadrant of space.

After surveying the surface of an alien planet, a transporter malfunction creates a duplicate of Osamu.

There's a time delay before the second Osamu appears, so it's not clear to anyone what's happened at first. Osamu seems tired and a bit disoriented, which is understandable after all the away trips to the surface, so Atsumu doesn't suspect anything right away.

They have separate quarters but an adjoining door, since they're brothers and all. Atsumu checks on Osamu that night when his shift on the bridge is over, thinking he'll get him some pudding and tuck him in. Osamu's worked so hard down on the planet and he deserves some rest.

Instead of finding Osamu in bed, however, he finds Osamu fresh from the shower, eyes glossy and the towel around his hips tented. Atsumu flushes, caught by his twin's heated gaze.

Osamu grabs hold of Atsumu and carries him to the desk, swiping everything off the surface.

Atsumu lands on his back with a thud, but he hardly cares when his brother drops the towel and has that /look/ in his eye.

The sex that night is rough and intense, like when they were teenagers fucking for the first time and getting addicted to that rush of pleasure.

The next morning, when Osamu joins him for breakfast in the canteen he is perfectly calm and composed, and seems surprisingly well rested. Atsumu is relieved. Guess their marathon did the trick, although he himself keeps yawning all through the meal.

His relief is short lived when Osamu keeps losing focus at his bridge post, daydreaming and fidgeting. When he asks Atsumu to repeat his question for the third time, Atsumu dismisses him to his quarters. Osamu slumps off, and Atsumu notices others in the crew exchanging looks.

The whole thing is embarrassing, but as Captain, Atsumu has to maintain the highest standards of conduct.

When he's off duty he goes to see Osamu to find out what's going on with him. One minute he's bold and decisive, the next he's passive and unable to focus.

He uses his palm print to open their adjoining door and stops dead in his tracks: there are /two/ Osamus in front of him. One is busy working up a sweat on a weightlifting machine and the other is lazily sprawled on a couch with a VR headset on.

/What/ in the seven intergalactic hells has happened here?

additional cw: selfcest, d/s themes, dubious consent/non-con, minor violence, #nsfw

Osamu lowers the weights on the machine with a clack and gets up, wiping his brow with a towel. "Fuckin' finally," he grouses, coming towards Atsumu shirtless and visibly flushed.

"Samu?" Atsumu looks between him and the Osamu on the couch lost in his VR game. He swallows.

Osamu's hand closes on the back of Atsumu's neck before he crushes their mouths together. Atsumu pushes on Osamu's chest, too confused and worried to make out--something really /wrong/ has happened and he's got to get to the bottom of it!

"Stop," he grits out, struggling.

"No." Osamu pushes him into the wall and gropes between his legs. "Need t'fuck ya."

Atsumu arches away from Osamu's hand, cheeks heating at the sudden rush of sensations he normally would welcome.

"Cut it out!" he insists, turning away from Osamu's kisses.

Osamu growls and bites him on the neck. "Yer off duty so just shut up and let me fuck ya!"

"No, Samu, not now!" Atsumu cries out, wedging his knee on Osamu's hip.

"Why not!" Osamu shouts. He bangs his fist on the wall, face in a snarl.

"I said t' hang on!" Atsumu pushes away.

He puts equal distance between himself and the Osamus. The one standing barefoot in loose sweats angles his body to close in slowly, while the one on the couch hasn't moved much except to curl further into the back of the couch like he's pretending they're not there.

"What the fuck is going on, Samu, why are there /two/ of ya?"

"Who cares?" Osamu scoffs, prowling closer. He points at the couch. /"He/ can do all the borin' stuff on this ship and I'll do whatever the hell I want. Now get back over here and gimme that ass or I'll /make/ ya."

Atsumu bristles at this, taking a defensive stance. "Yer gonna calm down, Samu, so we can figure this out. Cantcha understand the trouble we're in?"

"Cantcha understand that yer pissin' me off?" Osamu bares his teeth, closing in. "Got needs and yer gonna be good and satisfy me."

"Not until we know what the hell happened to ya and we getcha back to normal!" Atsumu shouts.

Osamu glares at him for a long, tense moment. Then he tsks and takes long strides to the couch, where he yanks the VR headset off the other Osamu, who yelps in fright.

"Hey!" he protests, arms crossed over his face protectively and knees drawing up.

"Guess ya have to do," shirtless Osamu sneers, swatting his counterpart's arms away and grabbing him by the shirt. "Get up!"

"Fuck off!" clothed Osamu snaps, squirming so the other Osamu can't

get a hold of him.

"Hey!" Atsumu steps in to intervene. "Leave 'im alone!" But he's ignored.

"Get. Up. Now." Shirtless Osamu grunts, struggling.

Atsumu grabs hold of Osamu's bare arm and tries to pull him off, but Osamu wrenches from his grasp and delivers a backhand-slap

so hard it knocks him to the ground. He blinks, momentarily stunned from the shocking pain, watching as shirtless Osamu drags the other Osamu off the couch to the floor and slaps him with similar brutality.

Osamu hisses, hunching over. Shirtless Osamu grabs him by the hair.

He tilts the man's head up, glaring as he works his sweats under his hard cock. "Hurry up and suck me off."

"'m not doing that again," kneeling Osamu grimaces, glaring back.

Shirtless Osamu abruptly delivers another two slaps in quick succession and kneeling Osamu goes limp.

He lets out a whimper, shoulders drooping. Shirtless Osamu wastes no time taking advantage of the other Osamu's pliancy to force his mouth open and shove his cock inside, hands holding his counterpart's head still against his steady thrusts.

Atsumu feels a pang in his gut.

He slowly sits up through his daze, trying to make sense of the incredible, bizarre sight in front of him.
Shirtless Osamu throws his head back and moans lewdly, muscles rippling as he fucks the other Osamu's mouth with abandon.

Kneeling Osamu just lets it happen; he's gone

utterly quiet despite the involuntary choking noises and drool around his mouth, or the tears leaking from the corners of his closed eyes.

Atsumu feels another strong pang--his body reacting to the opposing yet potent visuals of the two before him--and swallows, mildly sickened.

Atsumu gets up from the floor and turns away from the other men, taking halting steps to the doorway between their quarters and disappearing to the safety of his chambers. He closes the door behind him and rests on it, cathing his breath. But he's got to clear his head, he's

got to get his bearings so he can figure out what to do. He rushes out into the ship's corridor and walks briskly to settle his nerves, picking no real destination just needing to move his body and collect his thoughts.

He's worried about his brother, but he's also responsible

for the ship and the entire crew. If whatever this is has happened to anyone else on board, surely he'd have heard reports by now--a fact that offers a small relief. If the incident is isolated to Osamu, he might be able to keep it quiet while working on the solution and avoid

upsetting any of the other crewmembers and officers.

Lost in thought, he turns the corner abruptly and crashes into the solid chest of his chief of security, Aran.

"Whoa, Cap'n!" Aran calls out, catching Atsumu by the arms and righting him on his feet. "Whatcher hurry?"

Atsumu's face heats up in embarrassment, but he laughs it off and pats Aran on the shoulder. "Just lost in thought, sorry 'bout that. Nice reflexes."

Aran laughs with him and preens. "Wouldn't be yer Chief of security without 'em! Now what's gotcha in knots, if I may ask?"

Atsumu shrugs, waving a hand. "Oh it's nothin' much," he says, mind racing for an excuse.

Aran eyes him. "Sure I can't help ya with anythin'?"

Atsumu has an idea and snaps his fingers. "Actually ya can--mind tellin' the personnel director that Samu's takin' some time off?"

"'s he okay?" Aran asks, concerned.

"He's fine," Atsumu is quick to reassure. "Just needs some time off after that last mission. He's due a few days, so I granted permission."

"Got it, glad he's okay. Tell 'im we can spar anytime if he's up fer it!" Aran grins.

"Thanks, I'll tell 'im." Atsumu agrees.

They part ways and Atsumu exhales a deep breath, glad to have bought some time to figure out how /two/ Osamus are currently aboard the ship, both acting erratically. He takes a path back to his quarters and eyes the door to Osamu's.

Steeling himself, he enters Osamu's quarters. Neither Osamu is where he left them--he finds them on the bed, shirtless Osamu groaning and fucking into the other's rear. The other Osamu lies facedown in a heap, mewling, eyes glassy and mouth lax as if he's slipped into subspace.

Atsumu freezes in his tracks, taking this all in.

"Ha, back already?" says the Osamu who can still speak, leering right at Atsumu.

Atsumu notes that the other Osamu's clothes have been ripped off, though he lies there passively getting dicked down while drooling on the sheets.

There are finger-bruises around his wrists, and his bottom is flushed from a spanking, but he doesn't look too bad considering the potential for brutality displayed by the dominant Osamu.

Atsumu's body grows hot, flooded with discordant memories of being facedown like that while

his twin fucks him into sweet oblivion, or holding Osamu prone beneath him while he rams his cock into his needy hole. He touches his forehead, dizzy from the surging urges within him.

His brother must clock the desires coursing through him, for he lets out a deep chuckle.

"C'mere, Tsumu," he wheedles. "He's nice and ready now. Mouth's free, so go ahead. Dip yer cock. Feed 'im another load."

Atsumu wants to feel repulsed, but the suggestion is far too tempting, especially when submissive Osamu lifts his head, mouth open and tongue hanging out.

Subsamu whines, eyes still glazed.

Domsamu laughs. "See, he wants ya. Yer gonna deny 'im?" he challenges.

Atsumu clenches his teeth. He's a disciplined man but /this/ is something he's never been able to resist. He hurriedly undoes his uniform pants and approaches the bed.

Subsamu whines again, fingers digging into the sheets. Atsumu's dick is hard and leaking already, popping out from under his waistband. He holds Subsamu's head as gently as he can, and god help him--he thrusts his full length down the awaiting throat, moaning in pleasure.

TBC!

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