Pairings: Established Alpha!Yuuki/Omega!Zero and Alpha!Kaname/Alpha!Yuuki, with the romantic narrative arc working toward reluctant Alpha!Kaname/Omega!Zero, endgame Alpha!Kaname/Alpha!Yuuki/Omega!Zero, side Isaya Shouto/Takuma Ichijo

Anime only compliant, plus borrowings from manga canon.

Warnings for: weird vampire genitals (born female alphas and male omegas have both sets), people who identify as male but have a uterus and indeterminate genitals getting pregnant, body horror/dysphoria/disassociation (I'm not joking okay), explicit sex (probably poorly written and unrealistic, let's be honest), unhealthy mind-body relationships, possibly threatened non-con (it's an A/B/O fic okay), and significantly less dubcon than standard A/B/O universe (real biology is weird but the usual trope is not an evolutionary sound strategy so I messed with it)

I. Wind Up Boy

It takes weeks to clear away the rubble littering Cross Academy after the Rido Incident.

(Yuuki is gone. Zero feels like he needs to be scraped off the ground and carted away too. He wouldn't mind. His heart's been scooped out neatly with a spoon; knock on his ribcage and you'll hear a hollow ringing echo back.

This feeling never leaves him; he just learns to work around it like an old wound).

Eventually, once the chaos at the Association is sorted out, newly-minted Association President Cross sends him down to the research division for a full battery of tests. They need to know, he explains with concerned, yet kind eyes, just what has changed in his body now that he's completed his powers as a Hunter (murdered his twin brother).

So he submits to all the poking, prodding, MRI scans, skin samples, blood samples, spinal fluid samples - he's out of fluids to sample by the time the people in lab coats are through with him.

When he returns two weeks later to hear their results, the head researcher pulls him away to speak in private after they're through, then hands him one last folder to look at as she explains his condition.

Infertility. His body is unable to produce a single live sperm cell. They think, she explains to him with pity in her eyes, it's because he was turned so young, before his body and his reproductive system had time to mature, and after the 'disruption' things just didn't work the way they ought to. She expresses her condolences, and leaves.

It shouldn't matter. It should not matter.

But it does. It feels like he's losing his family all over again - like mother and father and Ichiru are cut open and bleeding out in front of him, and he's bleeding out with them.

He's always know he would never have a family of his own. He's a vampire; any children he fathered would be born vampires, and that is a fate he will never willingly inflict on another human being as long as he lives.

(Not that he lets himself contemplate exactly how many hundreds of years that may be, or compare how much shorter the lives of his remaining loved ones are.)

Not that he needed to think about children anyway. Zero was a vampire, and he would never be allowed to have access to a child as a single parent, even if Cross and Yagari supported him.

And thinking about a partner - it was useless. No hunter would even look twice at him; a sexual relationship with a vampire is the deepest taboo, even if he was born with the blood of a hunter the same as them, as ancient as any could claim, refined and tested for millennia through the Hunt.

Being with a human? No. Their lives are too different for understanding and connection. Zero does not want an empty relationship, or to raise a child in a place like that. And a human's life would be far shorter than his, a breath, while he stood unchanged in Time's flow. If he really loved his partner, Zero knows such a loss would destroy him.

And having a vampire as a partner - Zero cuts off that thought before it can finish (Yuuki was the only one he could ever love).

It really was best that Yuuki left him, wasn't it? Zero had nothing to offer her in the first place, except suffering as she watched him struggle against Level E and die millimeter by millimeter. Kaname could give her love, position, safety, wealth, acclaim, immortal companionship and joy - and now this was just one more thing the pureblood could offer her, and Zero could not.

It's not like someone whose inaction had killed his family, brought everyone who cared for him trouble, and hurt the one person he loved deserved anything else.

-Lilac eyes look down on him with hatred, accusations spilling from familiar lips, and a venomous final barb,

'It's your fault, brother...

...Tell me, did I taste good?'

- And Zero Kiryuu jerks awake, the scream on his lips suppressed through decades of practice in getting thrown out of apartments for disturbing the neighbors.

It's three-thirty AM, an hour and a half before he has to wake.

Zero doesn't really need an alarm; he hasn't slept through the night in over thirty years. He gets his rest in scattered snatches, three and four hour patches in between nightmares where all of his ghosts come out to remind him who and what he is. If he gets five hours of sleep he's being indulgent, and the following night will exact a price for being so weak. He wouldn't sleep in even if he could; that kind of peaceful, undisturbed rest doesn't suit a damned soul. Zero gets just enough rest that his Hunts' proficiency doesn't suffer, and no more.

This is his second nightmare of the evening; he won't be able to sleep again without wearing himself out first. So Zero gets up, lets himself out of his apartment, and goes for a run.

He doesn't need to change. Zero sleeps in his exercise clothing. It's more efficient than changing when he sweats through whatever he wears to bed, and they're suitable for more than one function. Pajamas are unnecessary; he owns exactly one pair to keep up appearances when sleeping at Cross' house or Kaito's apartment.

The neighborhood Zero lives in is caught in a downward spiral of the urban development lifecycle. It's bones speak of a once-wealthy residential district, now left to sag as it edges toward dismal neglect, the lonely trees with drooping crowns, dying or overgrown, the brown brickwork gathering stains, the concrete curbs crumbling at the edges without the city's money to repair them.

It's not a dump, and you couldn't call it the bad part of town, but anyone with money is starting to move if they can afford it, and the people left over are those who can't leave or don't have anywhere else to go.

Zero is both.

He needs to live close to his base at the Hunter's Association Central Headquarters for work, but in a town of Vampire Hunters, all the businesses and all of the residents could tell what was living next door to their children. It had been implied, when he inquired at closer complexes, that it would be best if he found accommodations elsewhere. Zero didn't hold a grudge. Trying to sleep when your Hunter Senses pinpointed a vampire nearby was like trying to ignore someone trailing a razor blade down your skin.

Eventually he found his current dismal lodgings in the next town over, with a human landlord. It means he has an hour long commute every morning and evening, but it was cheap and Zero saw no reason to spare himself inconvenience unless it affected his work.

Zero alternates between jogging and short walking breaks until the eastern sky has the faintest hint of light to his vampire sight. To a human it would still be pitch black, but Zero needs very little light anymore. The thought is still tinged bitter, even after nearly fifty years of living as a beast in human form.

Tonight was only the second worst kind of nightmare - things that had already happened, rather than mistakes and betrayals - people - he might still fail, or dreams of how he could have failed them even more than he actually had in their past.

This means he only has to run until his feet ache, rather than needing to run until he's dizzy and nauseous, and he heads back to his apartment.

Master Yagari calls it his closet, which makes Zero laugh because it doesn't actually have a closet. He never laughs for long, because Master will glare at him with worry underneath and it makes him feel guilty.

It's a single room, no kitchen, with a tiny cubicle of a bathroom. The floors are a yellow-brown linoleum, and the walls a dirty white color. The less he asks about the stains on either surface, the better, but his vampire nose tells him in great detail whether Zero wants to know or not. The whole complex smells faintly of decay, age, sunk in human smells from the threadbare hallway carpets, and smoke from a small fire about a decade ago.

Zero strips out of his clothing and steps inside to wash off the sweat. The shower - no bathtub - is a tiny square of tile beneath a shower head that's barely large enough to turn around in without hitting your elbows. The water temperature never goes above tepid. It's fine - Zero doesn't need it.

Cool autumn winds have left him chilled, so Zero gives himself an extra two minutes besides his usual five. The heating in his apartment hasn't worked since he'd moved into the complex, and the room is cold. It's not a problem; the Hunter just spends more time at the Headquarters in the winter.

All of the furniture wedged in the room - a narrow single bed with a saggy mattress, a plywood shelf unit with his personal belongings, a battered wooden table, and a plastic chair - has seen better days. None of it matches, and none of it was bought new.

Zero crosses to the shelves, wiping his face with his single towel, and takes his clothes for the day to dress. Most of the space is occupied by his Hunting gear - spotless, rigorously maintained, and top quality. The rest is paperwork, the two weeks' worth of clothes he owns and his spare blanket. The only personal items in the room are framed photographs, carefully hung, dust-free and well looked after.

Once he's dressed, Zero makes the bed with military precision, pulling up sheets which might have once been blue, but were now faded grey. They're poor quality, and scratchy with age. To sensitive vampire senses, it's like sleeping on a burlap sack. Zero doesn't bother using fabric softener when he washes them once a month.

Then breakfast - cereal, the bland, whole-grain fiber kind that even health nuts couldn't pretend was appetizing, no milk, and exactly fourteen almonds. There's no refrigerator to keep milk in anyway. He owns a rice maker and a microwave, which is enough to make the balanced meals of brown rice, red beans, and steamed vegetables that he prepares for every other meal he eats, tucked into food containers he packs into his gear bag. Zero eats exactly how many calories are necessary to maintain his body in top shape, and not a single one more. His body is the most important tool in his Hunting arsenal after all; it can't be neglected. This often leaves him finishing a meal with an edge of hunger, not quite reaching satiety, but it makes no difference to him.

(Zero allowed himself to cook exactly four times a year - on Christmas, and for Yagari, Cross, and Kaito's birthdays. He always makes sure he's on a long-term Hunt during his own)

Arming himself for the day is a little ritual of its own, a few moments when Zero reflects on his purpose and leaves him with clarity and focus, ready to begin the day.

First the chestpiece of light body armor, custom fitted to each individual Hunter. It wouldn't hold against a born vampire, but a Level D would need a few blows to do serious damage.

Then the weapons holsters, fastening around waist, thigh, ankle and forearm, snugged and tested to hold however Zero moved.

Now came the most reverent part. A dozen small daggers, perfect for throwing or for sinking into a weak spot. Then the Bloody Rose, ever faithful companion, most beloved. And last, against his thigh, his newest armament. Zero curls his hand around it a moment longer.

Winter, the recently rebuilt Cross Academy, Chairman's office. The fire flickers in the grate. Nothing is warm. Cross extends a hand toward him, holding Artemis' familiar handle.

"They were meant to be wielded as a pair."

Overtop all of that, the long pale overcoat, pockets filled with the rest of his kit - ammunition, basic medical supplies, a flashlight, and other necessities.

Then slinging his bag over his shoulder, Zero locks his door and makes his way downstairs to the well-worn but still serviceable motorcycle parked downstairs to make his morning drive.

His vampire does not like being out at this time of day; his whole body urges him it's time to sleep, the same way wakefulness comes easily to him in the night. The golden morning sunlight makes his skin prickle with discomfort; he's become more sensitive to the sun the older he gets, just like a real vampire. Zero ignores all of this with the ease of long practice as he strides into Headquarters.

Hunters may keep the late hours of their prey, but they're still human, and most of the staff still works daylight hours, which means there are plenty of people in the building who turn and watch him walk by as he passes through the halls.

Cross and Yagari have forcibly "retired" the filth left by the old president who saw Hunting as nothing more than sport, and anyone who would attack or demean him openly is gone, but no matter how many years pass the uneasiness bred in a Hunter's bones never goes away, and the eyes never stop following him, a constant reminder that Zero's nature makes him an outsider. A few of the old timers still glare silently. To the youngest ones he is a permanent fixture, allowed to pass into their world but not quite trusted or included.

The meeting he's attending this morning is a routine informational check in, so Cross and Yagari can get status reports on active missions, announce upcoming large-scale assignments and everyone can stay on the same page.

As always, Zero arrives early and stakes out an empty corner of the meeting room to stand in. Other hunters come in after him and gather together in knots or circle around the room exchanging greetings and news. There's a bubble of space around Zero's corner that nobody ever breeches, like an invisible barrier no one can cross. Zero has acquaintances and other Hunters he's friendly with, of course, and they call out greetings or come by to say hello, but no one ever steps into his circle or comes close enough to touch him, crossing that last bit of space into intimacy.

Zero prefers it this way. It's better for all parties if they don't get involved with him.

The meeting starts exactly on time as his Master and the Chairman file through the door and take their places on the podium at the head of the room.

Master Yagari looks old. There's no way around it. Anxiety weighs heavily on Zero's shoulders every time the revelation hits him anew. Fortunate vampire genes leave all elderly Hunters well-preserved for their age, and Yagari has many good years in him yet. But there's more grey than dark hair on his head, and Zero's Master favors his left leg just slightly, the mark of an old injury.

Yagari has remained an active Hunter well into his sixties, who still insists on being given missions and keeps up with the younger hunters as though he was their age. Yagari's field retirement isn't far off though. As loathe as his Master is to admit it, he doesn't bounce back as quickly as he did twenty - or even ten - years ago.

Zero secretly follows his Master every time the man goes out, shadowing him from just beyond the range of his (but not Zero's) senses, so he can watch over the man who is a cherished guardian and an important person to him. He suspects Yagari knows what he's doing, but tolerates it for Zero's sake and peace of mind. Besides, Master did the same to Zero for every mission he went on, solo or not, until his parents were killed.

Cross, of course, looks no different than he had the first night he'd taken Zero into his home, except perhaps a few new lines around the eyes, or his sandy brown hair growing a touch longer.

Zero is called on halfway to report on his current assignment, investigating a smuggling ring trafficking Level-D Feeders and searching for the Pureblood supplier.

Cross hadn't wanted to give him this mission; Zero could tell from the worried glances Cross gave him as he'd handed the folder over. Perhaps he'd thought Zero would empathize with the defeated, hopeless faces of other Level Ds turned just for their blood and treated like property, sold to other vampires who wanted a reliable meal source and maybe a little "extra" their bodies could offer.

The pureblood would never be arrested. No vampire ever would be brought to justice for anything that happened to a Level D with the consent of their Master. From the legal perspective of the Vampire Senate, the pureblood owned those turned humans and could dispose of them however they saw fit. The most Zero could do was find the human collaborators collecting the sacrifices and exterminate any Level Es he found as a warning.

So far he's found promising leads, but he'll have to travel to northern Europe to investigate the source.

Yagari doesn't immediately dismiss the Hunters when they've all reported in, which brings a stir of speculative chatter among the crowd since there must be an announcement forthcoming.

"Quiet, quiet," Cross flails his arms dramatically to gain their silence (but not as embarrassing as the way he did when he wore his Chairman persona; Cross lets his Hunter out whenever he's inside Headquarters).

"As some of you may have heard, the young Ichijo heir has presented as an Omega. Two months from now is his formal Presentation Ceremony. If his courtship is successful, ten months after that he'll hold a Rite of Bonding. This is the biggest event in vampire society since the Kuran wedding. We Hunters will be present to uphold our mutual treaty and most importantly, maintain our good relations with the vampires."

Yagari stepped up and continued in a drawl, "It will be all hands on deck, every spare Hunter we have assigned to keep an eye on the vampires, safeguard the peace and represent our strength. Don't do anything stupid and make us look like idiots. We'll update you with your specific assignment when we know. Dismissed."

As the Hunters file out of the room, dispersing to care for their assigned duties, someone too short to be seen over their heads is fighting against the flow, and heading straight toward him.

"Dr. Sawamura," Zero greets politely, as if that will make up for the weeks of avoidance and the inconvenience of dragging the doctor out of the medical center to seek him out personally.

The doctor is not dissuaded, and glares up at him, pushing her spectacles up her nose and dryly responding, "Kiryuu-kun. You've missed the appointment for your annual physical."

"My apologies Dr. Sawamura, I'm sure I'll make -"

"Three. Times." The elderly white-haired woman pokes him in the chest to punctuate her point.

Dr. Sawamura has ruled the medical staff with an iron fist as long as he's been alive, whether her position was official or not. Even with a pack of recalcitrant, stubborn Hunters as patients, not even Master Yagari dares to defy her.

She has also been his personal physician since he was a high-risk pregnancy in his mother's belly.

"How am I meant to look after your well-being if you won't come see me?" she scolds, then glares again.

"I've arranged for an appointment at this time. You have no missions assigned to you for the next two days. You will attend," she orders, and then frog marches him back to her domain.

Three hours later, Zero wobbles out of the medical wing dizzy, lightheaded, with shaking hands, and with his fangs aching something fierce.

Doctor Sawamura is supporting him with a hand under his elbow; Zero is embarrassed by the thought that the tiny old woman weighs two-thirds what he does and isn't breaking a sweat.

"-the cell cultures will be complete in two to three weeks. If we find anything we'll call and let you know. I'm ashamed to admit that even if we did find something, we have so little data on your situation it wouldn't help. We can track any systemic changes but we don't know what they mean in practical terms. I don't mean to alarm you. Your body seems to be settling into adulthood nicely, from what I can put together."

She fixes him with a concerned gaze. "You called someone to help you home before we started, yes?"

"Yes," Zero lies. No need to bother anybody; Zero would just hide in the archives and wait it off until he could leave.

Doctor Sawamura shoots him a significant glance that tells him he isn't fooling anybody, then remarks casually, "I think I see them now."

It's Kaito, somehow, and Zero darts a suspicious look at the doctor who is still keeping him upright and bearing most of his weight.

"Heard you needed a ride, you babyfaced teenage ass" Kaito calls out mockingly.

"Do you kiss your wife with that mouth, old man?" Zero jeers back at him.

"The divine Misao knew what she was getting into when she married me. Not allowed to curse in front of the kiddies either. Gotta get my fun in where I can." Kaito rocks back on his heels, strokes his short beard and raises his eyebrows suggestively.

Dr. Sawamura none-too-gently clears her throat, and Kaito jumps to take Zero's sagging form from her, looping his pale arm over strong shoulders.

"Thanks doc!" his sempai calls over his shoulder as he drags Zero away like a vampire's nipping at his heels.

Zero shoots a pleading look backwards; Dr. Sawamura only sighs and calls out, "Don't drop him Takamiya," just as they turn a corner.

Once they are safely out of earshot, Kaito's brisk pace slows down. "Whew, escaped the dragon lady in one piece, did you?"

Zero frowns. "Dr. Sawamura doesn't like you, Kaito, she's not like that with everybody."

Kaito manages to look disbelieving.

They continue in silence for a few moments before Kaito looks at him sideways, seemingly makes up his mind and demands, "Why didn't you call me?"

Zero cringes internally. Trust Kaito to be so blunt.

"We're both adults now, and you have responsibilities as a team leader, a husband and a father. You don't need to be spending time taking care of me anymore, sempai or not."

"You do know that I take care of you because you're my friend and my fellow student and you're important to me, right? You're not a bother. Hell, you never ask for anything. Dunno if I should be insulted or not. Really. Shows a real lack of faith in my skills."

Zero raises an eyebrow. "What skills?"

Kaito ruffles his hair in revenge, and just like that the serious air is gone. Kaito starts rambling about some sports team and how his kids are even more terrible than they'd been at that age, the noise making a comfortable background sound against his tired mind.

It takes Zero a few minutes to realize Kaito's quiet again and is studying him, dangerously observant, offering a glimpse of the brilliant Hunter who will one day take up Master Yagari's position.

His friend licks his lips nervously before looking him in the eyes and quickly asking, "Do you need 'that'? You look a little peaky."

There was only one topic that Kaito wouldn't tackle head-on when it came to Zero - the 'needs' that came with leading a parasite's cursed existence consuming the lives of others.

Zero is proud to say that not a single drop of blood has passed his lips since Ichiru's, all those decades ago. He subsists on blood tablets. His hungers are under control.

"No. I'm fine," Zero replies, and Kaito is kind enough to let the topic drop.

(Each pill is a struggle. Zero spent his formative years as a vampire denying his thirst so thoroughly, with such indomitable will, that his sense of hunger is permanently warped. He can't even recognize anything other than starvation; the sensation of normal hunger doesn't even register.

Then, when the need grows to a height where any normal vampire would have long yielded in desperation, torn open some human's throat and gorged on red heat, he pushes the ache a little further, always, because giving in without a battle means he's losing himself.

If he takes it when his hands shake and his muscles spasm and his body sweats and his throat burns in agony and his belly gurgles and he can't breathe because something is crushing his lungs-

- then he doesn't have to feel guilty. Then he's taking it not for Zero, but to keep everyone else safe from himself.

It's not bad at all, really. Zero has known the voracious, desperate, rabid thirst of the fall to Level E. The lesser hungers of a stable D-rank are nothing but sweet whims by comparison.)

A/N: I appreciate critique to help improve my writing. Thank you for reading!

The week of four Thursdays is a French idiom expressing an event that is impossible or unlikely to occur; it is equivalent to the English "when pigs fly" or "once in a blue moon."