Disclaimer: We do not own these characters. They are owned by BioWare and any other creators of the Mass Effect universe. We wrote this story as free, fun entertainment and do not mean to offend anyone.

Rating/Warnings: This story is going to be rated a strong MA+. This chapter probably doesn't deserve such a high level warning, but subsequent chapters will. I will try to warn for specific things as they come up in the chapter, but in general, this story takes place in something called an Omegaverse. For those of you who don't know what that is, it's a quirky little AU that developed in the Supernatural fandom and has since expanded to basically every other fandom out there. It fit nicely with our kinks, so we decided to try it.

In the Omegaverse, everyone can be classified in one of three groups: Alphas, Betas, and Omegas. Both male and female alphas have cocks (females get them when they're aroused, especially during an omega's heat), and possess the ability to 'knot' (tie themselves together) with their partner upon completion. Betas are basically the switches of this universe. They can mate with alphas and omegas, although they can't change their genitalia. Omegas are the bottoms. Both males and females have the ability to get pregnant, and they go through very intense heats, releasing pheromones that call all the alphas around them so they can find an appropriate mate.

As always, this is a femslash story that primarily features FemShep and Liara as our main romantic characters, if you don't want to read it, then you know where the back button is.

A/N: So, this is the highly hyped on Rae's tumblr Omegaverse collaboration fic. I, PC, must thank Rae for introducing me to the Omegaverse universe, something that jives very well with both of our kinks, as well as bringing me on board for this story. It was great fun to write with her and we both hope that you like it. We have actually finished writing this story, so there should be a chapter uploaded every day until you've got it all, and Rae will keep on me about it this time to make sure I don't slack off. Please feel free to leave us comments along the way, we both very much appreciate any feedback our lovely readers out there might have. Enjoy! Oh, and do forgive us for terrible titles, neither of us has a knack for thinking up any good ones.

Rae's A/N: 'Cat and I really didn't want to write yet another A/B/O story where the omega was terrified and helpless, so in our version, they're the ones with final say. Alphas might get violent with each other when fighting over a mate, but the omega gets to choose who satisfies their heat. Hurting or pressuring an omega to mate with you is highly stigmatized, which you'll see. Anyway, if this long intro didn't scare you off, I hope you'll enjoy! Get ready for some wonderful Omegaverse trash.

Omega's Choice

Liara's torment started with a soft, warm tingle at the back of her neck. The strange sensation was barely noticeable at first, so faint she thought she was imagining things. She only abandoned her terminal long enough to check the temperature gauge before returning to her research. Their encounters on Feros and Noveria had provided several clues concerning Saren's whereabouts, but the rogue SpecTRe was still at large.

You're just tired, she thought as she studied yet another ancient star chart, blinking blurriness from her eyes. You've barely slept since Benezia found peace in the Goddess's embrace. That's why you can't focus. But even though it was true that she had spent most of her nights working, the excuse sounded flimsy in her head.

Minutes later, the tingle became a searing flush, forcing her to unzip the collar of her green and white jumpsuit. Feeling air move across her overheated flesh helped, but only for a moment. She checked the gauge again, convinced it was broken. There was no other explanation for the burn crawling beneath her skin. The subtle twitching of her muscles. The curious fullness in her lower belly, slithering down to bloom between her legs. No explanation, except...

She shook her head and left her chair, refusing to entertain the thought. It's not possible, she told herself as she stood up from her chair. You're on a ship surrounded by humans. You aren't due for another three months. Your mother just died, for Athame's sake!

But no amount of protests could change her fate. She unzipped her jumpsuit another few inches, from her collarbone down to her sternum, and sat on the edge of her bunk. "It's going to be all right," she said to the empty room, staring up at the ceiling with pleading eyes. "I've been through this before. I can go through it again." Unfortunately, giving voice to her thoughts made the lies she was telling herself even less convincing. She crossed and re-crossed her legs, trying to get comfortable before giving up and flopping onto her back. She wasn't imagining things, and she wasn't simply sleep-deprived. The longer she suffered, the more certain she was. Her cycle was about to begin.

Liara remained flat on her back for several minutes, paralyzed with confusion and fear. Her previous heats had come at regular intervals, and she was always able to prepare. Locking herself away for a few days was inconvenient, but no more so than ending up in bed with the nearest available alpha and conceiving on accident. As an asari, she was even more likely to make a mistake than most other species. While humans, turians, krogan, and most other sentient races could only reproduce with their own kind, the meld gave her body the ability to process and understand alien DNA. With a sufficient sample and a strong mental connection, she could easily conceive in a moment of weakness.

"Maybe it won't be so horrible this time," she said, but the shaking statement sounded anything but certain. Another surge of warmth flashed through her, and she gave up trying to stay clothed, tearing open the diagonal line of her zipper and pushing the fabric down to her waist. "Maybe my scent won't affect humans as strongly as other asari. They might be able to ignore me." But somehow, she doubted she would be so lucky. There was a reason everyone else called asari the sirens of the galaxy. Since they were able to breed with anyone, their heats were powerful enough to call almost every species. And here she was, stranded on a human ship without any recourse. All she could do was ask Doctor Chakwas to provide her with sedatives, lock herself away, and suffer. Unless...

No, she thought, not even daring to speak that idea aloud. I couldn't ask her. It would be too awkward. Too embarrassing.

Her breath hitched anyway, and the coiling sensation in her abdomen twisted even tighter. A dark, warm stain began to soak through the fabric between her legs, and she kicked her jumpsuit the rest of the way off. It was already ruined anyway. Instinctively, she rolled onto her stomach and cupped a hand between her thighs, whimpering as wetness painted over her palm. She curled into a ball, trying to ignore the hollow ache.

"Shepard..."

The name pounding in her brain slipped out before she could bite it back. She tugged her lower lip between her teeth as soon as she spoke, but it was too late. Saying it aloud felt like an admission of guilt. Come to think of it, Shepard was probably the cause of her unscheduled predicament. Her body had likely reacted to the Commander's powerful presence and come into heat early. Although she was soft spoken and endearingly sweet in private, her dominant aura was unmistakeable. Anyone could tell she was an alpha from a hundred yards away. The way she stood, the way she spoke, the way she smelled...

A fresh spill of slickness coated Liara's fingers, and she buried her face in the mattress, sobbing with frustration. Touching herself wouldn't do anything to ease her pain, but she couldn't stop. Her fingertips began circling the ridge of her clit despite her better judgment. As unsatisfying as it was, masturbation was the best option. Her muscles quivered, and her hips picked up a slow rocking motion.

It was only the image of Shepard's face floating in her mind's eye that interrupted her rhythm. She pulled her glistening fingers away, ignoring the trails that slid down her thighs. Her own hand was useless, no matter how many orgasms it provided. There was only one solution to her problem - or, at least, one solution that wouldn't leave her vulnerable. She needed to clean up, get dressed, and see Doctor Chakwas as soon as possible so she could beg for help.

Shepard was leaning against the weapons bench, chatting casually with Ashley Williams when the scent hit her nose. The first trace made her body stiffen, and her sentence trailed off as she forgot what she was saying. She turned toward the elevator, closing her eyes and inhaling deep. There was no mistaking that thick, smooth, honey-sweet smell. No other scent she knew of could seep into your body and light a fire there. She swallowed, trying to get rid of the moisture rising in her mouth. Her eyes opened, and she turned back to Ashley Williams. "Is that...?"

She didn't need to finish her question. Ashley had a similarly entranced look on her face, and her tongue darted out to run over her lower lip. "Uh-huh. Damn it. Looks like we've got a problem, Skipper."

'Problem' is a bit of an understatement, Shepard thought. A shudder coursed through her, and her clit twitched as all the blood in her body rushed to fill the swollen bud. Despite her better judgment, she inhaled again. The scent was even sweeter the second time around, and a deep growl vibrated in her throat as it settled on her tongue.

"Who do you think it is?" she asked, trying to ignore the uncomfortable pressure in her pants. The throbbing grew worse by the second, and she gripped the weapons bench again for support. Despite her best efforts, the aching shaft of her clit began to extend. Her eyes darted around the cargo hold, searching for the source of her torment. "Not Alenko again, right? According to the roster, we don't have any other omegas assigned to the Normandy." But she already knew it wasn't Alenko. She had definitely noticed his last heat, but it hadn't affected her with even half as much intensity. He wasn't her preferred gender, or even her preferred personality type.

It took a moment for Ashley to respond. When she finally did, her voice was low, throaty, and raw with tension. "No. Doesn't smell like him."

"It's not me," another voice said. Shepard whipped around to see the subject of their conversation approaching. "I had my turn two months ago, remember? It's not time yet." He paused, sniffing in the direction of the elevator. "Whoever it is, they've got it bad. They're broadcasting like crazy."

Shepard didn't need Kaidan to point out the obvious. Her length was already pointing far enough on its own. The shaft of her cock strained against the front of her fatigues, growing thicker with each breath she took. As impolite as it was, she had to reach down and adjust herself to ease the pressure. "This isn't fair. There aren't supposed to be any other omegas on board," she complained, almost pleadingly.

"You know some of them hide." Shepard turned to see Garrus approaching from the other side of the cargo hold. The turian had abandoned his position by the Mako to join them, and from the quivering of his mandibles, she could tell he had scented the omega too. However, he was still faring much better than Ashley. The gunnery chief had followed her example and clutched the weapons bench to maintain her balance, and she almost looked ready to pass out. "With enough drugs in their system to disguise their hormones, they can pass as betas. Either this one concealed their status, or they didn't need to register in the first place."

A dizzying thought struck Shepard all at once. There was only one possibility on the ship. One person who could easily have a strong effect on the entire crew, regardless of species. One person who had no reason to register with the Alliance brass. She let out a loud groan as the fullness pulsed even more painfully along her shaft. Without wasting another second, she rushed for the elevator, Ashley and Garrus right on her heels.

She nearly crashed into Tali on the way there. The quarian let out a yelp of surprise, darting out of her path just in time. "Keelah, what do you think you're doing? Are you crazy, or..." She paused, and the filters on her suit whirred. "Someone's in heat again? I thought Kaidan was the only omega on the ship?"

"Already been over that," Garrus said, a little testily. "Someone lied, or it's-"

Shepard ignored them, fumbling with the pressure pad. She had to get to the med bay. Had to get there before anyone else. Had to...

"No time," Ashley grunted. "Get out of the way, Tali."

The doors to the elevator finally hissed open. Shepard edged in first, but Ashley's shoulder collided hard with her chest on the way. Garrus followed, and so did Tali, looking half-confused and half-entranced. Shepard snarled when she took a step too close. Although most betas would never turn down an omega in heat if they could find one, they didn't have the same primal drive to claim. Except for Kaidan, Tali was the least of her worries. Ashley and Garrus were far more obvious threats.

"Don't take it personally," Kaidan said as Tali edged toward the other side of the elevator. "They don't mean it."

"Stop apologizing for them," said yet another voice. Shepard's lips peeled back over her teeth when she saw Wrex's large hand come up to hold the doors open. He stepped inside as well, making the whole lift shake with his weight. "These young varren pups call themselves alphas, but they don't have any self-control. One fertile bitch has them humping the walls and climbing over each other to knot her."

"Oh, really, Wrex?" Kaidan gave the krogan warlord a sly look. "That isn't what I remember from last time."

Wrex snorted, shaking his giant plates. "Heh. True enough. But compared with these idiots, I'm the model of self-control."

The doors finally closed, and the elevator started to ascend. Shepard bristled, resisting the temptation to pace. She felt confined in the small space, and the delicious smell was growing stronger. Her mouth watered as she imagined tasting the salt of hot, naked flesh, and her length pulsed. Worse still, the heavy breathing beside her set her on edge. Ashley and Garrus were both quivering with want, and even Wrex seemed to grow a bit dazed the higher they climbed.

After what felt like an eternity, the lift ground to a halt. They ran from the elevator as soon as it opened, but stopped short soon after. There was hardly any room left to walk. Almost every member of the Normandy's crew was crowded into the mess, gathered outside the medbay. They jostled one another, trying to reach the door and peer in through the tiny window. Others hovered along the glass wall, stealing glimpses since they didn't stand a chance at getting to the front entrance.

Shepard didn't have to join them to know who was inside. Liara.

The ache between her legs doubled, and her focus narrowed to one goal. She had to get through the others and into the medbay. She grunted, shoving her way past Ashley and Garrus and flaring her biotics. The crowd before her parted, but only reluctantly. Most of the betas who had been drawn to the window scattered, but the alphas near the door didn't budge until she got in their faces. "Move," she snapped, forcing Silas Crosby to retreat with the strength of her stare. Talitha Draven glared right back until she let out a warning rumble and showed her teeth. Even once they stepped back, they remained as near as they dared, unwilling to sacrifice even the slimmest chance of claiming the prize within.

"Keelah, this is worse than Kaidan's last heat," Tali said, weaving her way through the crowd to join them.

Ashley's shoulders stretched broader at her appearance, and her eyes narrowed to slits, but Garrus gave her a warning shake of his head. "Don't," he forced out, the flange in his voice tighter than usual. "You'll regret it later."

"The turian's talking sense," Wrex boomed, stomping through the remnants of the crew. They had to move because of his sheer size, although none of them looked happy about it. Shepard had to suppress a growl of her own as she noticed that Wrex finally had the same problem as the rest of them. An uncomfortably large bulge was pushing against the front of his pants, and the mere sight of it made her bristle. There was no way she would let Wrex, Ashley, or any of the others near Liara. "Get a grip, Shepard," Wrex said, clapping her on the shoulder. She gave him a disgusted look, but he only laughed. "No reason to be jealous. Yours is pretty impressive. For a human's, I mean."

"This isn't a fucking joke, Wrex," Shepard barked, whirling back to face the door. She slammed her fist against the pressure pad while Garrus and Ashley crowded in on either side. It blinked red. Locked, of course. Dr. Chakwas wouldn't dare open it until the problem was under control. "Damn it," she swore, even though what remained of her mind was relieved. Poor Liara was probably frightened. Normally, omegas prepared well in advance if they knew they would go into heat in such a confined space. To experience one on an alien ship without access to proper care had to be terrifying.

"Give it a minute, Commander. The doctor will solve this problem. She has to have something in her medicine cabinet to dull Liara's signal."

But the mere thought of losing the scent made Shepard hurt. Not just the heavy shaft between her legs, but all over. She needed Liara like she needed to breathe. Her eyes ached at the thought of not being able to see her. Her mouth throbbed to taste her. Memory-snatches of Liara's lovely voice sang in her ears. Every inch of her skin burned to feel Liara's flesh. With the door closed, she couldn't have any of those things, and the thought of losing her smell too was unbearable.

"Liara…"

When she rested her forehead against the metal door and let out a strangled sob, even Ashley and Garrus weren't foolish enough to disturb her.