Author's Note: I am back after a very long hiatus. What's more, I'm going to dive right in and write a smutty Captain America/Avengers fic with lots of smut. This couldn't be helped, however, since I am also grounding this story in an AU Omegaverse. So, let's dive right in, shall we? 18+ONLY!

This is the first time I'm publishing/writing smut, A/B/O, and after a very long period of radio silence. So, please be gentle with me in the reviews but, at the same time, leave some please : ).

Ultimate Omega

– A Captain America x Bucky Barnes x Reader Story

Part I

Hydra Compound

Blinding light. Voices yelling. Your mind was foggy. Your arms were strapped to the back of the chair you were sitting on. You blinked and saw the blurry shapes of Captain America and the Winter Soldier in front of you. They were chained to the wall; their limbs incapacitated by thick metal rings. Steve was on the left and Bucky on the right, a door between them. Their heads resting limply on their broad chests.

What were you doing here?

When the white room came more into focus, you realized that the voices came from people in lab coats scurrying around you. A sharp pain in your neck made you tense up and your head shot up. You glared at the person who had just jammed a syringe into your neck.

"What…," you tried to speak while struggling with your restraints. But by doing so you moved your left foot and a piercing pain shot up your leg which knocked the wind out of you. You winced and gritted your teeth.

"Steve, Bucky? What is going on?" you said, voice hoarse.

Both of them raised their heads. Apparently, they had been knocked out or drugged in some way and were just now coming back to their senses like you. The man with the syringe slapped your cheek.

"Don't worry, sweetheart", one of the lab coats said. "It'll all be over soon."

You blinked frantically but the fog in your head wouldn't dissipate so easily.

"Is she ready?" a different man in a dark uniform asked.

"Yes, she is, Commander. The Ultimate Omega serum, we injected her with earlier, is already changing her system. I just boosted her pheromones one last time. There is no way two Alphas will not tear each other limb from limb over this new creation."

Both men in white looked warily at the two super soldiers still chained to the wall. You took a deep breath to calm your nerves and smelled something unfamiliar.

"This means we need to get out of here, Commander." The first man continued. "Her smell is going to drive them crazy any minute now."

"Understood, Doctor."

Both men gathered the remaining test-tubes and files and left through the door between Steve and Bucky. Unbeknownst to one of them, a set of keys fell silently out of his pocket in front of you. The other lab coats were following hurriedly after the two men and then closed the door. You could hear the lock sliding into place and suddenly the room felt very quiet. All you could hear was your heartbeat in your ears and Bucky's panting.

"Steve," he growled, "I can already scent her!"

Thoughts were rushing through your head. What did they do to me? What is that smell? Did Bucky actually just… growl?

A sudden burst of pain in your stomach made you keel over.

"It hurts so much," you whined.

"Stay calm Y/N," Steve said. "We need to get out of these chains, Buck!"

You heard both of them struggling with their confinements. They knew they needed to help you. Your vision became a little clearer but a stabbing in your abdomen made you see little specks of light dancing around your eyes. You felt abnormally hot; it was as if you were running a fever. You groaned and looked at the two super soldiers in front of you. You saw them straining against their chains, their muscles bulge, heard their grunts and… growls? There was that sound again but you couldn't be sure of what you perceived. And what was more, you liked that sound. Confusion written all over your face you fidgeted with your restraints. You needed to get out of here.

With one loud thunk and an even louder cry Steve could free himself from one of the chains pinning down his right wrist. Part of the brick wall had come off which was now hanging from the chain.

"Y/N, do you see those keys in front of you?" Steve said; you could hear the strain in his voice. "Kick them over to me. You can do it!"

He moved his now free hand towards you and angled his body so that he was as close to your position as he could possibly get. Steve frowned when he saw your injured foot; blood trickling down from the wound. But then he saw you using your right foot and urged you on. You glanced at the shining set of keys a few inches in front of you.

Thankfully, you were barefoot. Thus, you were able to grab the keys with your toes, kicked your leg up and surprisingly accurate flung them into Steve's hand. The friction of the movement between your legs made you take in a sharp breath. It felt as if you were getting… wet; but here? Now? How was that even a normal reaction to all the danger you were in? What did these people do to your body? Did you just see Steve inhale and his eyes turn dark, almost black?

He was looking at you intently. Then he started inserting various keys into different locks on his chains.

Meanwhile Bucky's grunts continued. Finally, he was able to tear down a piece of the wall too with his metal arm. He pierced you with his gaze and was breathing heavily.

Your head slumped onto your chest; the strain from the key toss had been too much in your fragile state. More cramps hit your stomach. You heard the noises of Steve freeing himself, chains clinking. In your mind you imagined that you could smell them. Their heavy scents, their sweat, their arousal? This couldn't have been real, could it?

You glanced at Bucky while Steve was freeing him from the chains. He looked as if he was ready to pounce on you; his pupils blown.

"Guys, what is going on?" you asked hesitantly, toppling over in pain again.

Steve had already freed Bucky's other arm and squatting down was now trying out different keys on the chains that held Bucky's legs.

"Steve, they made her an ultimate Omega. They changed her DNA. I'm not even sure that she was part of our world before. Mm, she smells so good," Bucky licked his lips involuntarily.

While unlocking the last lock on Bucky's right leg Steve replied, "Snap out of it Buck. Because of her healing abilities we might not have sensed what she is before. But now she's definitely an Omega."

A growl escaped Bucky's lips. As soon as Steve had freed him, he took two long and swift strides and knelt in front of you between your knees. He cupped your cheek with his flesh hand. His other hand was placed on your thigh.

"Y/N, look at me. How do you feel? Can you heal yourself?"

Steve knelt behind you freeing your wrists from the medical restraints that resembled belt buckles.

You moaned. It felt as if Bucky's hand on your leg was sizzling hot and each time Steve's fingers touched yours behind your back it sent short bursts of electricity through your body.

"It hurts," you whimpered.

"I know it does, little Omega," Bucky said. "We are going to make it better."

What did he just call you? Omega? That's what these Hydra people had called you. You remembered now. You had accompanied the two super soldiers on a rescue mission into the Sokovian mountains to extract a possibly hurt SHIELD agent.

Steve said, "They did this to her to make us fight over her. Over who would be her Alpha. Do you smell that, Buck? She's already in heat!"

You felt Steve smell your neck, right underneath your earlobe. You leaned into him. He was nuzzling into your neck and pressing feather light kisses to your skin. A shiver ran down your spine and goosebumps spread all over your body. You moaned.

Steve had freed your hands but they just hung limply at your sides.

"Look at me Y/N," Bucky said. "I know this might sound crazy to you but what these people did was alter your DNA. They turned you into one of us – well not exactly."

He took a long but shaky breath to steady himself. Both of his hands were on your thighs now; his metal hand travelling dangerously higher on your leg.

"Steve and I, we are Alphas. They made you an Omega."

Steve who was still behind you swept your hair over your right shoulder and continued licking and kissing the area around your collarbone.

"An ultimate Omega," he murmured into your skin.

Your breathing got heavier.

Bucky continued, "When an Omega is in heat, an Alpha will always respond to that – to the scent."

Once more he inhaled deeply, pulling himself closer to you between your legs. You felt the straps on his armor at the inside of your thighs. There was a lump in your throat and you swallowed slowly.

Steve's hand had circled around your waist and was now spread out on your belly.

"Alphas often fight over who would be able to claim an omega first," Bucky's flesh hand traced along the line of your lower lip.

You looked at him with hooded eyes and a slightly open mouth. Why did this feel so good? It should feel wrong. You had escaped your chains but you were still inside a HYDRA base and why hadn't this fog from the drug they had given you lifted yet? You still felt as if in a daze.

"Claim?" you whispered while Bucky was stroking your chin.

He replied, "Yes, claim. It means who will have the privilege to mate with you first."

Realization dawned on you. Was he serious? Another wave of pain gripped your abdomen and you saw white light behind your eyes. You felt dizzy, light-headed.

Steve stopped his ministrations on your neck and pressed his hand on your stomach.

He growled, "Buck, we need to do this now. Her first heat could kill her. You don't know the side-effects this HYDRA-drug could have."

Bucky tensed. He knew Steve was right but hearing it out loud didn't make it any better.

"Y/N, look at me," Bucky begged.

You willed yourself to look into his eyes. They were dark but oh so beautiful. His metal hand slowly traced a line on your thigh to your core.

"I know this isn't what you bargained for and under different circumstances we would certainly do this differently. But we need to make sure that you survive this. And there is only one way."

He pressed his flesh hand into your soaked core and you almost screamed in ecstasy. Steve's hands had found their way to your breasts. He massaged them through the thin layer of your SHIELD uniform and you couldn't help but arch your back and press yourself into his palms.

"What is it that you need to do?" you panted and then swallowed hard.

"You need to have sex with one of us," Steve whispered into your ear.

How could this sentence send shivers through your spine and turn you on at the same time? This was ridiculous but it was oh so right at the same time.

You felt the base of Bucky's thumb draw circles on your clit over your soaked trousers. You groaned.

"So, who's it going to be, little Omega?" Steve continued rubbing your now hardened nipples through the fabric of your shirt.

At that exact moment you heard shuffling and muffled voices outside. Steve's head shot up and he stopped his ministrations on your body. You whimpered from the loss of his touch.

Bucky looked at him but didn't stop the movement with his hand. You desperately wished that there was less clothing between the two of you.

"Buck, you need to do it. I don't think she's in any state to truly decide," Steve got up. "Besides, you and I are mated, so there's no risk of me doing what HYDRA wants me to do. I'll keep watch. I'll protect the two of you."

"Are you sure Stevie?" Bucky whispered while you pressed yourself into him, whining and longing for more than he was giving you.

Steve nodded and in one swift move Bucky had gotten up and pulled Steve's head towards him for a passionate kiss. You sluggishly moved your gaze and watched them, the desire for both of them spreading through your body like wildfire.

"Help me carry her to that stretcher over there," Bucky said.

Steve lifted you up bridal style while Bucky was shrugging of his jacket and continued with his pants. Steve laid you down on top of the stretcher, immediately taking off your clothes. If his touches hadn't felt like the only remedy for your burning heat, you would have questioned his actions or felt exposed.

In the blink of an eye you were fully naked on your back on that stretcher and looking at an equally buck naked super soldier between your legs. You could see his throbbing erection amongst the rest of his muscled glory. From the corner of your eye you could see Steve checking and barring the door with what he could find.

"I'm here doll," Bucky said. "I'm going to make you feel so much better. You're gorgeous, little Omega."

He kept calling you that strange word but honestly at that point you didn't really care. All you wanted was him all over you. His hands, his body, his scent. You wanted to be his.

Bucky pulled your body at your hips to the edge of the stretcher towards him. You pushed yourself up and took his face between your hands. Looking into his deep blue eyes, you felt the stubble on his cheeks. Then he crushed his lips against yours and his chest against your breasts. Never in your life had you experienced a kiss like this. Every touch of his tongue sent sparks through your whole body. His hands were roaming your back and moved to your hips, when you felt his erection between your folds. Both of you let out a gasp of pleasure. Bucky drew in a sharp breath and then gently pushed you back down again.

Steve, still in full Captain America gear, had come over and stepped next to you. You could see the bulge between his legs. Instinctively, you reached for it and rubbed him over his combat pants. He growled. Bucky let out a chuckle when he positioned his face in front of where you wanted him most. You looked into his hooded eyes between your legs as he started parting your lips with his tongue. A small whimper escaped your mouth whilst still stroking Steve through his pants.

He had to grip the edge of the stretcher to steady himself. Steve watched intently as Bucky's tongue flickered over your nub and your body started convulsing in ecstasy, making the sweetest noises.

Steve couldn't take it any more and pulled out his swollen shaft dripping with precum. You spread it around his tip, earning a sharp hiss from Steve, and started pumping him.

Bucky held your thighs spread apart with his hands and continued delving his tongue into your folds.

"Bucky… more," you moaned and could almost feel his grin against your flesh. Your wish was his command.

He continued lapping up your slick while inserting a flesh finger into you. A slight hiss escaped your lips but it was exactly what you needed. Steve had started thrusting himself into your hand now, groaning in ecstasy. Ever so gently, Bucky inserted a second digit into your burning flesh. You whimpered in pain for a second, freezing all your movements. Bucky paused for a moment letting you adjust. Realization hit him.

"Steve, she's a virgin," he said in amazement.

Steve's eyes became round and then almost instantly clammed shut when you resumed stroking him. You pushed yourself onto Bucky's fingers which he took as a sign. He curled his fingers upwards into a come-hither motion and continued licking your clit.

"Yeah, that's the spot I was looking for, girl. You're so wet for me."

All your nerve ends felt on fire. You felt your orgasm approaching.

"Yes, I can feel it. You're almost there, baby girl. Come for me my sweet little Omega, I know you can do it."

And with those words you were driven over the edge and so was Steve. Fireworks exploded in front of your closed eyelids while Steve spilled all of his seed onto your belly. His grunts mingled with your screams. Both of you were panting heavily when Bucky reemerged from between your legs. He stood up with a wide grin on his face and started licking up your calf. He trailed featherlight kisses over the inside of your thigh and over your mound. When he reached Steve's sperm, he lapped it up eagerly, dipping his tongue inside your bellybutton. You moaned at his actions.

"Move up a bit, doll. It's my turn now," he said hungrily.

Like a feral animal Bucky climbed on top of you and onto the stretcher, while you shuffled upwards. He placed his metal arm on the right side of your head and vice versa with his other arm as to not crush you under his weight.

You felt his erection press against your entrance. Instinctively, you wrapped your legs around his waist. Tentatively, you looked between the two of you and saw that he was huge. You swallowed and looked up into his eyes again.

He must have felt your reluctance because he whispered, "I know you haven't done this before. I'm here for you. You can trust me. But I need your consent my little Omega." He growled, pressing his tip a bit further into your entrance. "Do I have it?"

He kissed and then sucked your skin along your jawline. When he felt you nod, he crushed his lips onto yours and buried himself deep within you in one swift thrust. You gasped into his mouth, overwhelmed by both pleasure and pain alike.

After a short moment, Bucky started moving inside you and you felt the heat in your belly rise up again immediately. Briefly, you sensed Steve who had returned to his position at the door, fully clothed again. But then Bucky's thrusts drowned out your surroundings completely. You heard his pants in your ear while he was sucking on your earlobe.

"You feel so good, Y/N. Fuck!" he almost screamed.

Bucky had found his rhythm now and slammed into you relentlessly.

"You need to knot her now, Buck!" Steve shouted from the door. "We are running out of time!"

Bucky growled. As you felt your second orgasm approaching you could also sense movement inside of you apart from Bucky's frantic thrusts.

"Oh, baby, this is my knot. Can you feel it?" Bucky panted. "You can take it. I'm almost there. Come with me."

Whatever it was you were feeling was deliciously grinding against your G-spot. All you could do was succumb to the feeling, to this man, your Alpha inside you? You stumbled over the word in your mind but were immediately carried over the edge by Bucky's pounding. You screamed until your throat hurt and your vision turned black. You arched your back and pressed yourself into Bucky who took two more thrusts before spilling his seed inside of you. You felt him pulsing inside of you and listened to his uneven breathing in your ear. Slowly you came down from your high, still panting heavily. You stared up into Bucky's eyes at a loss for words.

"Wow your scent could ignite a whole pack of Alphas, Y/N," Steve said looking at you from his position at the door. "How long do you think your knot will last, Buck? What do you think? We need to get a move on."

Still looking into your eyes, Bucky murmured, "Give it a few minutes, Steve. Are you alright, doll?"

You swallowed and nodded your head, not knowing how to respond. You had just had mind-blowing sex with that gorgeous man on top of you who was still somehow inside you.

"We need to stay like this for a bit longer," Bucky continued. "If I pull out now, my knot would most definitely hurt you."

"Your knot?" you asked uncertainly.

He caressed your cheek and then said, "I'll explain all of this later to you, I promise."

Bucky planted a soft kiss on your brow, then slowly and carefully turned the two of you over. You were now lying on top of him, still connected at your most vulnerable parts. Bucky gently stroked some sweaty strands of your hair away from your forehead. He smiled at you. Never in your life had you felt so intimately linked with anyone – body and soul – than you did just then.

Steve on the other hand was getting anxious, you could sense it. Both of you turned your heads towards him. Now, that the stupor you had been in, started to lift, you noticed your surroundings again. The gleam of Steve's shield. The smell of the sterile room. The aching in your foot.

The noises outside your door got louder. You could hear impatient voices but couldn't quite make out what they were saying.

A few moments later, you felt Bucky slip out of you. He gave you a last peck on the lips, then rolled away from under you. As fast as he could, he put on his uniform and then grabbed the gun Steve was holding out for him. Why hadn't these stupid HYDRA agents disarmed them completely? They had said something about Steve and Bucky killing each other or had that been part of your hallucinations?

You scrambled up and made a move to get down from the stretcher. As soon as your left foot hit the floor though, you let out a piercing scream in agony. If Bucky's metal arm hadn't caught you, you would have crashed to the ground.

"Shit, Steve!" he cried. "She has a shard of vibranium in her foot. Can you hold her steady while I put some clothes on her?"

The two super soldiers had you basically dressed almost as quickly as they had you undressed before. You winced when you tried to put your foot on the floor again.

"I can't heal with this metal still inside of me," you said. "But I can't walk like this either. Leave me here and get out, the two of you."

Both super soldiers scoffed.

Bucky said, "Not a chance, sweetheart. Alphas will always take care of their Omega, no matter what."

And with these words he had swept you up in his arms.

Steve put a hand to your cheek, "We are going to get out of here together. Trust me."

He quickly stole a kiss from you before barging through the door, guns blazing and with Bucky right at his heels with you in his arms. You hugged your arms tightly around Bucky's neck and closed your eyes, hoping this would be over soon.

The last thought, before gunfire drowned out your senses, was about your two super soldiers and their safety. How could you survive without any of them now?