John wasn't sure what he expected when he stepped into the lab, but it certainly wasn't what he saw. Admirals Hood and Osman were arguing quietly with each other and a terrifyingly calm Doctor Halsey, with a dozen or more scientists looking on, trying and failing to act like they weren't eavesdropping from their workstations. The Spartan paused for a moment to sweep the room, cataloging all weapons and exits, then approached the trio.

"...you are intelligent, Serin, and I will not disrespect you by implying otherwise," Halsey was saying, "You know as well as I how many eyes are on this project, how much is riding on this being a success - and how many people would love for even the slightest excuse to defund the entire program, regardless of the potential fallout."

"Those idiots in the budget office don't even know what the consequences would be," Osman growled quietly, so quietly that John was certain none of the eavesdroppers heard her.

"Indeed. Thank you for joining us, John," Halsey said when he stopped and saluted, "The rest of you, out."

"And if any of you breathe so much as a word of this to anyone, you will be on ONI's shit list from now until the end of time," Osman added.

Several scientists swallowed thickly, but all of them were quiet when they scurried out of the lab. When they had gone, Hood sighed. "At ease, son. We've got a bit of a situation on our hands."

Those words made the Chief tense up more than the actual summons to the lab. After his and Cortana's narrow escape from the destruction of the Didact's ship, Doctor Halsey had come and whisked the dying AI away before anyone could tell her "no". It had been almost a year since then, but he hadn't received any word from either of them until now. The rest of Blue Team had convinced him that no news was good news, but Hood's words brought all that tension and worry rocketing back.

"Sir?"

"Cortana is still with us, John," Halsey said, "but right now we need to know if there has ever been a time where you were working closely with her, had her in your armor while you were off your suppressants."

For a moment the Spartan blanked. What did that have to do with this? Still, he dutifully answered, "Yes, ma'am, during the Battle of Alpha Halo up until our return to Earth. The MJOLNIR's automatic injections ran out, and the refills were destroyed when the Autumn crashed. We only had the standard ones."

Which were better than nothing, but because of their various augmentations, standard military suppressants really only functioned as a scent blocker for Spartans - for his generation, at least. He wasn't sure about the S-lVs, but for everyone else, the suppressants blocked scents - pheromones emitted for various reasons - as well as ruts and heats, and it also functioned as birth control for those who could carry children.

The officers and scientist exchanged glances that made a knot of anxiety form in his gut. Then Halsey turned back to him. "How much did Déjà teach you about secondary genders, John? Did she teach you all about involuntary mating?"

Uh oh.

"Just the basics, ma'am; we weren't ever supposed to go off our suppressants except for the once-yearly... season, to maintain our health."

In addition to determining primary biological sex, the "sex chromosomes" also carried markers which determined a person's secondary gender - Alpha, Beta, or Omega. The Spartans had been trained well, but John would have needed a doctorate in genetics to explain the complicated web of dominant and recessive, presenting and non-presenting ABO markers. What he had been told was that everyone inherited two markers, one from each of their parents, though usually only one presented. Beta was the most common presented marker, though not overwhelmingly so, and the majority of the S-lls had been Beta-presenting, including Serin herself and Doctor Halsey.

John had been one of only five so-called "thoroughbred" Alphas among the S-lls, having inherited an "A" marker from each of his parents. Most people would - and did - take pride in being "thoroughbred", but he hated it and knew that Fred did as well, and the others had, too, before their deaths. The other Spartan Alphas had all been AB, which made their ruts much milder. With a finely balanced cocktail of scent blockers, they could ride it out together or even work through it.

The thoroughbreds didn't have that option. Their ruts made them stupidly aggressive and territorial and therefore absolutely miserable; the Spartans had been trained as a pack, and being separated from the group or even just their own squad made them bitterly unhappy.

"I can't say she taught us about involuntary mating," John continued, "Or if she did, it's been long enough that I've forgotten, ma'am. Is it... what it sounds like?"

"To a certain extent, though probably not the way you're thinking," Halsey replied, "When was your last rut?"

The Spartan swallowed and said, "July 2549."

All three of them squinted at him, which he resolutely ignored. Then Halsey said, "I suppose we'll just have to be grateful for that, then. I can only imagine what kind of disaster it would have been if we had discovered this earlier."

"It might still be," Serin said, pinching the bridge of her nose for forestall a headache.

To John, Halsey said, "Involuntary mating is a rare phenomenon now - almost everyone is on suppressants - but it has been known to occur when highly compatible individuals work closely together for an extended period of time while off suppressants. They can become chemically, hormonally, and pheremonally attuned to one another to the point where they are biologically mated without ever consummating the relationship and exchanging the so-called "mating bites" - or even without there ever being a relationship at all."

The Spartan blanked again, then said, "Cortana and I are involuntarily mated?"

"So it would seem."

"All right. So what's happening? Why is that important?"

"We'll get to that in a second. You're taking this very calmly."

"As far as I'm aware there's not much we can do about it now, ma'am."

"Indeed." The scientist eyed him for a moment, then continued, "I'm sure you're well aware of how badly off Cortana was when you were retrieved from the Mantle's Approach."

The Spartan nodded. The blue and pink static had been a constant haze at the edges of his HUD by the time they'd arrived on the Infinity, coupled with whispers in his ear that ran the full spectrum of emotion. On top of that, his armor's function had been... glitchy. Abrupt starts and stops, sudden lockups or even shutdowns, unexpected pressurization and depressurization of the hydrostatic gel layer... It had gotten so bad that Cortana had told him to eject her chip, and though that had been the last thing he'd wanted to do, he had obeyed.

"Given her state, I didn't believe recompiling her into a new AI was a viable solution," said Halsey, "Instead, we decided - and she agreed - to test a new procedure where an AI is implanted in a flash clone. Our understanding of genetics and cloning has grown greatly even just over the past several years, so we've been able to eliminate many of the defects that have plagued previous generations. We'll still be keeping a very close eye on her - probably for the rest of her life. I understand it may be a bit of a shock, but the procedure was a complete success. She implanted in the host body with no problems."

It didn't take any great leaps of logic to see where she was going with all of this. "She's in season?"

"Unfortunately, yes." Halsey frowned deeply. "We intended to start her on low-grade suppressants before she presented to give her more time to adjust, but I was forced to let others handle some aspects of her care. Those doing her bloodwork weren't keeping a close enough eye on her hormone levels."

Her expression said she wouldn't soon forget it, and Serin's matched. Hood just looked tired.

"We've been doing what we can for her since then, but her heat hasn't ended," the scientist finished.

Which was a sure fire sign that she was mated; mated pairs' heats and ruts could last up to five times as long if they were apart during it. "Emergency icers?" Meaning the suppressants meant to stop a heat or rut after it had already begun. On the few occasions he'd had to take them during the Human-Covenant War, they had been thoroughly unpleasant but very effective.

"Both of us are allergic, though which kind causes which reaction seems to change from year to year. I would rather not play guessing games with her life."

"She needs you, son," Hood said finally, "but if this isn't something you want, we won't force you."

"Though it is highly encouraged," Serin added.

That started the two of them arguing again. Halsey ignored them and led him to an isolation chamber at the back of the lab. He hated the damned things - white, cold, soulless - and he hated them even more when he saw Cortana curled up on a mattress and pile of blankets in a corner. From what he could see of her, she looked pretty much the same as she had as a hologram, just human now. Her dark hair even had a slight blue tint to it.

"What is she?" he asked quietly.

"OA."

His eyebrows shot up at that. Omega-Alphas and their Alpha-presenting counterpart Alpha-Omegas were not quite the rarest configurations (that dubious honor went to the thoroughbred Omegas), but they were the only configurations that were actively courted to serve in the UNSC, and received a great many benefits for doing so. AOs and OAs both had the fighting power and instincts of an Alpha without the territoriality and ingrained resistance to taking orders, and the pack-bonding and protectiveness of an Omega without being prone to evasion and escape, flight rather than fight.

But then John frowned. He knew that Halsey was a BA, a Beta-Alpha, so where had Cortana received her O from?

He quirked an eyebrow at the scientist, who sighed quietly. "It's a little late now, but… before I gave her to Jacob, Miranda used to tell me that she wanted a sibling."

Ah. John nodded in understanding. But then he hesitated. "Do you... think she'll let me?"

"I would be genuinely surprised if she didn't."

He nodded again and stepped toward the airlock into the room.

The scent hit him like a MAC round. He had no real words to describe exactly what Cortana smelled like to him now - nothing except contentment. Safety. Home.

But there was an undercurrent of distress that made him smother a growl. Instead of hunting down the scientists who hadn't been keeping a close enough eye on her biochemistry (another thing he didn't want to think about), he entered the attached bathroom and dug around for a washcloth, ignoring the sting of the injection site in his arm.

Most people took about seventy-two hours to clear their suppressants if they just stopped taking them. A counter-injection brought that down to twenty-four hours.

He would clear his in six hours. Hopefully that would be enough.

The Spartan returned to the main room, noting that Doctor Halsey had put down the privacy shutters, and had to smother another growl at the thought of all those scientists watching Cortana as she suffered through her first heat.

Then he frowned. He shouldn't have been this protectivepossessive of her so quickly.

Maybe they really were mated.

He set that aside for now in favor of wiping Cortana down as gently as he knew how, careful not to hurt her new body. She had already suffered enough, and he didn't want to be the one to cause her more pain.

("LIKE HE IMPRISONED HIS PROMETHEANS?! LIKE DOCTOR HALSEY IMPRISONED ME?!")

When she was as clean as she was going to get without him actually giving her a bath, he tucked her back into the nest she had made, rinsed the washcloth, then dampened a different one and laid it on her forehead to try to keep her temperature down. He had a vague memory of his mother doing the same for him a long time ago, so he supposed it was worth a shot.

It didn't actually take her too much time to come back around. His scent was probably starting to filter through already, because she distinctly sniffed the air, frowned, and forced her eyes open to squint at him.

He realized then that he didn't know if she had ever actually seen his face. But she had heard him speak before, even though he was usually characterised by his silence. "Cortana."

She relaxed at once, and smiled up at him. "John," she said softly, "I missed you."

"I missed you too."

Her smile widened. Then she stretched and resettled with a sigh. "I don't understand how you can do this every year," she mumbled, rolling onto her side to face him, "Well, everyone else, anyway."

"You knew?"

"Who do you think helped you change your records starting in 2550? It wasn't exactly hard to see that you were miserable. Now I know why." She frowned again and let her eyes drift shut. "Did Doctor Halsey tell you?"

"She did, though not the how."

"Working theory is because I was borrowing some of your wetware via your neural lace," she hummed, "Compatibility has to be high for it to work; otherwise bad things could happen - to both of us. Needless to say, the UNSC's put a mandatory halt to any AI-unmated Spartan pairings until further notice, unless it's an absolute emergency."

"Probably for the best." He brushed the backs of his fingers over her hair. It was the softest thing held ever felt. "Though we're not exactly in high demand now that the war's over. Supposedly."

Cortana snorted, and her smile returned. "Ah yes, the hypothetical end of the war," she said, her voice as dry as a desert, "along with the supposed end of your missions."

"You've been reading my after-action reports." It wasn't a question, not really. In fact, he'd expected it.

She opened her eyes again and gave him a mischievous smile. "I might not be an AI anymore, but I still know my way around."

He felt a smile of his own tugging at his lips. Everything had changed, but she was still very much herself.

"I've missed going out with you, though," she continued, "You always did take me to such nice places."

"Even with all the murderous aliens?"

Cortana laughed at that. "Yes, even with them. Though I'm sure you understand when I say I never want to go anywhere I might encounter the Flood again."

"Agreed," John nearly growled. He remembered the Gravemind and the damage it had done all too well.

He laid down next to her, right at the edge of her nest, but she pulled him into the blankets and tucked herself against him with a contented sigh.

"The Gravemind," she said softly, sleep already setting in again, "While I was on High Charity, he tried to get me to go over to the Flood of my own free will and promised me something like this in exchange. This is much better than anything he showed me."

"There is something to be said for reality and truth, rather than the illusion of them."

John shot back to full awareness the instant Cortana whined against his throat. He let out a soft rumble in response, trying to soothe her while he took everything in.

Isolation chamber. Lights were low; his body clock told him it was somewhere between midnight and one AM. Cortana was in his arms, human now, smelling of home and distress and a rising metallic scent he'd always associated with a plasma bombardment. It was coming from the former AI; the Spartan had cleared his suppressants, and her heat was ratcheting higher in response, trying to spark him into a rut.

It was definitely working. He could feel his temperature starting to rise, sweat breaking out on his skin and heat pooling in his gut.

The Spartan shook the AI awake. "Cortana."

She too rocketed back to full awareness, blinked, and then started spitting some of the most foul language he'd ever heard. She'd paid more attention to the ODSTs than he'd realized.

When she took a breath to continue her tirade, he interrupted, "Do you want me here? I know we're technically mated, but if this isn't something you want, I can go."

"What the fuck kind of question is that?" she nearly snarled. She threw herself at him, forcing him to catch her, and took the opportunity to slam him onto his back in their nest. "Are you saying that because you don't want to be here?"

"Cortana, if I wasn't willing, I wouldn't have even entered the room. I've just never done this before."

That made her soften a little. "Well neither have I, so this can be a learning experience for both of us."

Their first kiss was awkward but gentle - neither of them knew 100% what to do - and it lasted for only a short while before Cortana shifted to bury her nose in his throat, scenting him. He found her hands with his own, and laced their fingers together palm to palm to let the scent glands on their wrists rub against each other, mixing their scents, marking each other.

The former AI nearly purred at that, then sat back and tugged at his shirt. When he obliged her and stripped, her hands felt cool against his chest, even though he knew she was burning up.

But then she giggled, and John quirked an eyebrow at her. "You're softer than expected," she said, running her hands up his chest and then down his arms, "I suppose I thought you'd be hard like your armor - a slightly fleshy boulder, I guess - but I don't know why I thought that."

"No frame of reference?" he suggested right before she leaned down to kiss him again.

"Maybe," she murmured between kisses, "Doesn't explain why it carried over though. Come on, soldier, clothes off."

"Still no frame of reference; I haven't exactly been able to drop by for you to check," John half-growled, toeing off his boots, "and it's kind of hard to get undressed when you're sitting on me."

Cortana shifted off of him with reluctance, and he unbuckled his belt, then shoved everything else off in one push. He'd barely laid back into the nest before she was back on top of him, this time examining his scars. There were plenty to choose from various surgeries and nearly thirty years of constant warfare.

Her own skin was completely unmarked, aside from a few small dots in the crooks of her arms where the needles had gone in for her bloodwork. Soft, too; certainly softer than his own - except perhaps there.

"Gently," he managed when she shifted further back onto his thighs so she could take his half-hard cock in hand. Her touch was gentle, curious more than anything, and her hands were very different than his own, smaller, not rough with calluses from decades of training and warfare. She seemed to enjoy the roughness though, if her response to him rubbing his thumbs over her nipples was anything to go by. Still he made an effort to be as gentle as he knew how while his hands roamed her skin.

Cortana didn't seem to complain, exploring him as much as he was exploring her, before she decided she'd had enough of foreplay. She leaned forward to kiss him again, then shifted up and forward and back down again.

John threw back his head and gritted his teeth hard enough that his ears rang, his whole body locking up to stop from thrusting up. But Cortana was shaking above him, and he sat up on one elbow to hold her close, support her weight. "You all right?" he managed gruffly, his voice at least an octave deeper than it already was.

She nodded against his throat and gasped, "Fine. Just - intense."

The Spartan was inclined to agree. She was perfect around him, and hopefully he was for her, and he wanted to stay there for the rest of time. "Let me know when you're ready to move."

She did. It took them a bit to find their rhythm, but they did and moved together as easily as they always had. Alpha instinct wanted John to reverse their positions, put Cortana on her back in the nest of blankets, but he ignored it in favor of supporting her weight, helping her move on him and being mindful of his greater strength. She was no civilian, he could tell just by looking at her, feeling the strength of her grip; Halsey had done something to her, genetically engineered her flash clone in some way, but she wasn't Spartan-level augmented. He still had to be gentle.

But not too gentle. As before, she enjoyed a little manhandling, gave as good as she got. He rumbled deep in his chest, and she growled right back, a playful grin on her lips.

Then she gasped and tossed her head back, her whole body arching and blue-black hair flying as her climax took her by surprise - and him, when it dragged him over the edge with her. John clutched her close to stay buried inside her as his knot expanded - but he didn't bite until she did.

It took less than a minute for their racing hearts to carry the pheromone markers in their saliva up into their central nervous systems. And just like that, tension John hadn't even realized was there bled away.

"Well, that certainly explains why your cortisol levels have been so high for the past year," said Halsey, intently reading the results of the scans she'd run on them both when they'd finally worn themselves out, "I can't imagine that mating bond your body perceived as one-sided was doing anything good for your health."

John acknowledged her with a quiet hum, and when Cortana squeezed his hand with her own, he squeezed ever so slightly back.