Fate/Charm of the Devil Fae

This fic is inspired by Sticky Situation by  Professor Quill,   In Bloom by Flight of Fancy,  and to a certain extent Benefits of Saving a Veela by WD_ONeill . Please check them out.

Story Starts

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Ch. 1.3

Sheathing Protocols

Disclaimer: Everyone here is at least 18 years of age. In Japan, students are typically 18 years old during their last year of high school. So all scenes of a sexual nature were done between consenting adults.

But to be safe, let’s add an addendum: this is a major AU. After Senior High School, students generally go to an academy for one to three years to take general subjects, think honestly about what they want, and prepare for higher education, or take vocational courses. This will take place during that period.

Shirou’s base level ' Charm’ is more akin to a Veela’s aura; it lowers the inhibitions of people who are attracted to Shirou, but ultimately, it’s up to them whether they want to act on it. It also depends on their general level of promiscuity.

In this story, both Sakura and Rin are fraternal twins, and I’m not going through the Illya-is-a-legal-loli route, nor will I ever—not that there’s any wrong with young-looking or petite adults.

'So… this is awkward,' Shirou thought, the understatement of the century echoing through his mind as he maintained his seiza position. His knees pressed against the tatami flooring with increasing discomfort, the woven straw digging into his skin with every passing second, a constant reminder of the utterly mortifying situation he'd found himself in.

Here he sat, attempting to preserve some shred of dignity after that utterly passionate romp with his former homeroom teacher—the annoyingly energetic pseudo-older sister who had barged into his life, a consequence of Kiritsugu having contacts with the local mafia—and the unapologetic mooch who seemed to think his home was some sort of all-you-can-eat establishment. The memory of what they'd done, of how they'd basically debased the sacred area of his kitchen, sent heat rushing to his face in a fresh wave of mortification.

The way they'd sprayed their release across every surface as if an artery had been severed, marking his territory with their shameless desire in glistening trails that still haunted his imagination despite the magical cleanup…

The kitchen counter, the carefully prepared dashi he'd spent the morning perfecting with such reverence, and even the ingredients he'd already meticulously cut with his best gyuto knife—all of it had been thoroughly contaminated by their unbridled lust. That was putting things lightly, he thought with no small amount of internal despair, the phantom scent of their coupling still lingering in his nostrils.

Thankfully, the situation had been easily reversed when Rin had snapped her fingers—mirroring Runeas's actions a few minutes before—with that infuriatingly smug expression on her face, magic rippling through the air like cool water to cleanse every surface of their mingled bodily fluids, leaving the kitchen pristine once more.

Though, naturally, for Rin's own twisted amusement, she'd deliberately left his own fluid-soaked clothes in their sullied state.

So here he was now, completely naked, his still-stiff member hidden beneath his strategically positioned hands as he clung desperately to some sense of decency in front of this assembled audience. His legs were already turning numb from holding this formal position for so long, pins and needles beginning their cruel march up his calves like fire ants under his skin.

Meanwhile, Taiga remained shamelessly dressed—if one could call it that—in her scandalously revealing lingerie, her modest breasts jiggling with every animated gesture, rosy nipples completely exposed to the air as she cheerfully asked Sakura for another helping of rice as though nothing remotely unusual had transpired.

Shirou winced as he brought another piece of the salmon to his mouth. The piece of broiled cured meat was perfect—the taste, the texture, the flaky tenderness—the problem was the lingering traces of devil magic on the fish. Typically, this wouldn't be a problem, but Shirou's nose was particularly sensitive to anything magical, a type of synaesthesia where he associated certain smells with different kinds of magic. And with every bite came a particular sulphuric aftertaste as he chewed the fish, a faint reminder of Runeas's intervention that made his stomach twist and his cheeks burn anew.

Everyone ate quietly, chopsticks clicking against porcelain in a rhythm that did nothing to ease the thick tension hanging in the air like humidity before a storm, the silence broken only by the occasional slurp or swallow.

Sakura moved with practised grace, refilling Taiga's bowl before the woman could even formulate the request on her lips. Her oversized shirt—something she and Rin had almost certainly pilfered from his wardrobe after waking, judging by the size—slipped precariously down her shoulder with each motion, exposing the elegant curve of her collarbone and the faint flush still lingering on her pale skin.

She caught him staring, and rather than looking away in embarrassment as she might have done years ago, she smiled knowingly at him, a secretive curve of her lips that made his chest tighten with something he couldn't quite name—guilt, desire, affection all tangled together in a knot that pulled tighter with every glance.

Rin sat cross-legged opposite Sakura, thumbs moving rapidly across her phone screen as she texted someone—something quite amusing, really, considering she had been absolutely helpless with any modern technology the first time they'd met all those years ago. Now she navigated it just the same as anyone her age, though she still occasionally held the device at odd angles—distrusting anything new or unfamiliar, like the time she had to record one of the shows he'd been following because he was still cleaning the archery dojo back in Homurahara, her frustration with the remote control still a fond memory.

"This is delicious, Sakura!" Taiga's voice shattered the delicate silence like a hammer through glass, her enthusiasm utterly at odds with the suffocating atmosphere, her cheeks still flushed from exertion as she beamed. "Even better than usual! Did you do something different with the seasoning?"

"Don't speak with your mouth full," Rin muttered without bothering to look up from her screen, her tone carrying that particular brand of exasperation reserved specifically for Taiga. However, the corner of her mouth twitched with reluctant amusement at the woman's complete lack of shame.

Taiga swallowed hastily, nearly choking in her eagerness to continue. "But it's true! Whatever you did differently this time—the tamagoyaki is absolutely magnificent!"

Sakura merely smiled serenely, that same enigmatic expression that gave nothing away, and thanked Taiga politely as she, too, continued to finish her portion of fish.

After Shirou had been unceremoniously sent to the proverbial corner—forced to sit seiza in the living room like a chastised schoolboy—Sakura had taken it upon herself to continue preparing the breakfast he'd started, her movements calm and precise despite the chaos.

Shirou shifted minutely, his legs screaming in agonised protest beneath him. The position was absolute murder on his circulation, pins and needles spreading through his calves with increasing intensity like fire ants marching under his skin, and his member had finally, mercifully begun to soften, though it still twitched traitorously whenever Sakura leaned forward to serve more food.

Her loose shirt dipped each time she moved, the neckline gaping to offer tantalising glimpses of pale flesh still flushed pink from their earlier activities, skin he could still feel beneath his fingertips if he concentrated—the memory of her warmth, her softness, her quiet moans sending unwelcome sparks through his body even now.

As Runeas set her chopsticks against the hashi-oki with deliberate, elegant care, she swept her gaze around the seated group gathered around the living room's chabudai, those violet eyes—ancient and knowing, gleaming with centuries of mischief and wisdom—meeting Shirou's amber stare directly. She winked at him with shameless amusement, her tongue moistening her full lips in a slow, deliberate glide that made his breath catch in his throat despite everything, despite the mortification still burning through his veins like molten iron, leaving him flushed and fidgeting beneath the weight of her knowing smile that seemed to strip away his remaining defences.

And then, with a casual wave of her hand, every dirty dish flew into the sink with barely a whisper of sound whilst the rest glided gracefully towards the recently repaired dining table, moving as if carried by invisible, perfectly trained servants who knew exactly where each porcelain piece and utensil belonged in the household's familiar rhythm, for a being like Runeas magic was simply a part of them just as much as breathing does.

With a single sharp clap that echoed through the tension-thick air like a judge's gavel, cutting through the lingering awkwardness with decisive authority, all eyes turned towards the ancient former matriarch of the Gremory family—the former minor goddess approached by Lucifer himself in ages long past, Runeas Gremory of the original seventy-two pillars, her presence commanding the room with quiet, undeniable power that made even the air seem to still in respect.

She was also Shirou's magical guardian, the devil Kiritsugu had called in absolute panic as the boy he thought he'd saved was engulfed in cursed flames that wouldn't die, that devoured flesh and magic alike with relentless hunger until Runeas had arrived to contain what should have killed him outright.

Shirou remembered fragments of that night in vivid, painful flashes—the searing agony that had consumed him, the raw terror in his eyes as he realised his rescue had failed, and Runeas's steady, unflinching gaze as she analysed the impossible situation with cool precision.

That was the night his fate had been sealed as a devil-fae hybrid—the queen piece embedded within him as its corrupted power mingled with Avalon in a violent, unstable dance, the two artefacts battling something primal and ruinous that still lurked beneath his skin like a sleeping beast, a constant reminder of how close—

"Shirou," she began, her voice carrying that particular tone that brooked absolutely no argument—interrupting his thoughts—rich with centuries of command and laced with fond exasperation, "this is something everyone has already discussed far away from your aura after they've properly relieved themselves of certain... tensions. So I don't want to hear any of your whiny excuses, okay?"

Shirou had the decency to look away in embarrassment as he mumbled his apologies, the heat in his cheeks intensifying under her direct gaze and the weight of everyone's attention. After the complaints he'd heard from both Rin, Sakura, and Taiga—the fact that his isolation had only made things worse for everyone around him, turning his attempt at protection into a burden that affected the entire household—he knew resistance would be pointless, the guilt and embarrassment settling in his chest.

Runeas leaned forward with deliberate slowness, her elbows settling onto the chabudai with the practised ease of someone who had spent centuries commanding rooms just like this one, though presumably under vastly different circumstances—palaces of devils, courts of fae, battlefields long forgotten, the weight of history in every graceful movement. Her violet eyes—ancient and knowing, gleaming with the weight of millennia—swept between the Tohsaka twins with an expression that managed to occupy some indefinable space between clinical interest and maternal concern, as though she were simultaneously conducting a medical examination and checking in on beloved daughters she'd watched grow across lifetimes. The weight of her gaze was palpable, making the air feel heavier somehow, charged with the subtle hum of power that always seemed to follow her like a shadow, drawing every eye in the room without effort.

"So then, how was the experience, truly? You started—what? Around mid-morning, if I recall correctly, and around what time did you actually finish? I want specifics."

Rin tried valiantly to play it cool, her chopsticks pausing halfway to her mouth in what she probably hoped was a casual gesture, a single grain of rice tumbling back into her bowl with a soft plink that seemed loud in the sudden hush. But the flush that crept up her neck—blooming from her collar to her jawline in a deep, betraying crimson—had absolutely nothing to do with the steam rising from her rice, and everything to do with the memories that Runeas's question conjured, vivid flashes of tangled limbs and breathless cries that made her shift uncomfortably in her seat, the lingering ache between her thighs a reminder she couldn't quite ignore.

"We... we finished close to midnight using all the stamina potions Taiga brought," she admitted, her voice straining for nonchalance and missing by several miles, cracking slightly on the last word as fresh heat flooded her cheeks. "The food helped as well, though honestly, without those potions I think we would have collapsed somewhere around round two."

"Every last one of them," Sakura confirmed quietly, though her voice carried an undertone of satisfaction that made Shirou's ears burn with renewed intensity, the heat spreading from his face down his neck in waves of mortification that pooled low in his belly, the memory of her creative use of shadow tendrils still fresh enough to make him tense.

"Freak," Rin teasingly whispered—the reason was due to Sakura's… umm… creative use of her magecraft during sex, those shadow tendrils that had wrapped and teased in ways Shirou still felt phantom echoes of, drawing a knowing smile from her Sakura.

Sakura's fingers traced idle, abstract patterns on the table's surface before winking at Shirou as he felt another one of her tendrils wrapped around his member—albeit briefly before vanishing—his body visibly tensing, a sharp intake of breath betraying him as Rin narrowed her eyes while Sakura adopted an innocent look that fooled no one, the brief touch sending an unwelcome spark through his already overwhelmed system.

"The entire case. We went through all twelve vials. Though I suspect..." Sakura paused, her dark eyes travelling from Shirou to Runeas with that enigmatic glint that always made him uneasy. "Though I suspect that Shirou could have gone for considerably more if he really wanted to."

Runeas's perfectly sculpted eyebrows climbed towards her hairline, genuine surprise flickering across features that had probably witnessed countless impossibilities over her extraordinarily long existence, before settling back into composure. "That was twelve vials of concentrated stamina restoration," she said slowly, as though testing the words on her tongue, the implications sinking in, "and we also made absolutely certain the food was calorically indulgent."

"We would've needed significantly more if we hadn't gotten sleepy towards the end," Rin interjected, her voice steadier now but still carrying that tell-tale huskiness from exhaustion and satisfaction. Then her expression shifted, becoming suspicious as she shot a pointed glance at Shirou. "And thank you for the vial of Phenex tears, by the way, it helped relieve certain aches."

The way she said it made it clear she knew exactly where that particular resource had come from—his deal with the Phenex clan after he'd defeated Riser in one-on-one combat, an agreement that was still a secret—only known to him, Runeas, and the current Gremory and Phenex patriarchs and matriarchs still hovering in diplomatic limbo, the knowledge hanging between them like an unspoken promise.

Which was precisely the main reason he'd run away when Rias had offered her own... solution to his problem. He couldn't afford entanglements with the Gremory heiress, not when the arrangement hadn't yet been resolved, the political implications too tangled for his already complicated life.

It'll probably be soon settled, judging from the news he heard from Runeas a month ago, the thought sending a fresh wave of anxiety through him.

He locked eyes with Rin across the table—but he shook his head minutely, a silent plea that carried the weight of shared secrets and mutual understanding. Rin, to her credit, shrugged, knowing she'll probably learn of it when the time comes, her expression softening with reluctant acceptance.

"Hmm... fascinating data points," Lady Vivian murmured, speaking properly for the first time since the discussion had begun. She was the only other being present here probably as old as Runeas—give or take a century or two, though with entities like them, time became rather abstract. Her crystalline eyes studied Shirou with the detached interest of a researcher examining a particularly intriguing specimen, though a faint warmth softened the clinical edge, acknowledging the young man beneath the curse. "We might need to experiment systematically with what the minimum amount of... relief... Shirou needs daily is before he reaches a critical threshold, and precisely how long the effects last before Shirou reverts to losing control of his aura. Establishing baseline requirements would be invaluable."

"Oh... we can certainly arrange that this weekend," Runeas interjected smoothly. "After all, we still need to test out the specific effects of his semen on various subjects—the magical properties are still largely unknown, and we should establish proper documentation. Sakura and Rin, I'll definitely need your help then as primary test subjects, plus young Ajuka promised he'll have everyone's evil pieces delivered by then. The timing works out rather perfectly."

"Finally," Rin declared with genuine relief flooding her voice, her posture straightening as though a weight had lifted from her shoulders, the tension in her frame easing visibly as long-held plans clicked into place. "I could convert Ayako now." She turned to Taiga with genuine curiosity, brightening her features with a spark of excitement that cut through the lingering awkwardness. "How about you, Taiga? Will you ask Shirou to convert you? Join his peerage officially?"

Taiga smiled as she turned her attention to Runeas instead. "I've already agreed to being Runeas's pawn, actually. We discussed it last week."

Runeas hummed thoughtfully at that, then shifted topics with the casual air of someone discussing weather patterns rather than the complete restructuring of someone's living situation and magical allegiance. "Speaking of stamina and long-term arrangements—you should really see what we've accomplished with the estate whilst you were moping Shirou. I'll be sending for our special builders from the Gremory territory—once the final plans have been properly reviewed and finalised."

"The old Emiya residence has grown considerably—exponentially, really. We've acquired all the surrounding land through various perfectly legal means—every plot, every abandoned lot, every square metre within a three-block radius. So everyone can request and plan for their own dedicated workshop space. Proper facilities for everyone's specialised needs."

A paper materialised in her hand with a casual flicker of devil magic that made the air shimmer momentarily, reality bending just slightly to accommodate her will with the ease of long practice, the parchment appearing with a faint scent of brimstone. The parchment crackled as she unfolded it with deliberate care. "Which brings us directly to this—the deed transfer. Officially signed over from Kiritsugu himself."

Shirou's breath caught painfully in his chest, his heart suddenly pounding against his ribs like a caged thing desperate for escape. "He actually—he signed it over?"

"He's finally made proper contact with Touko Aozaki," Runeas explained, her expression growing more serious. "They'll probably be thoroughly indisposed for the better part of the year. Possibly longer. It was part of the deal when he requested my assistance."

"Now then," Runeas's tone shifted again, carrying that particular note of absolute authority that brooked no argument, no negotiation, no escape, the words settling over the room like a verdict from on high. "About the arrangements going forward. The new household rules, as it were."

"Ah, our sheathing protocols," Lady Avalon interjected with a mischievous lilt that drew a faint sigh from Runeas.

Runeas ignored this but Shirou could hear a slight exasperated tone in her silence before she continued. "This estate—specifically the main residence where we currently sit, where we share meals and living space—has been officially designated as what we're calling a 'relief zone.'"

Shirou's confusion must have shown plainly on his face, his brow furrowing as he tried to parse the implications with growing dread, because she elaborated with clinical precision that somehow made it worse, her voice steady and matter-of-fact despite the bombshell nature of her words. "Simply put, within these walls, you can have your way with anyone who resides here, no conditions, no guilt required or expected. No scheduling, no permissions needed, no complicated negotiations or advance warning. Spontaneous relief whenever the need arises. That also works both ways, naturally—anyone can initiate with you. It has to be fair, after all."

Shirou's mouth opened, closed, opened again like a fish drowning in air. No sound emerged from his throat despite his best efforts. His brain had apparently short-circuited entirely, overwhelmed by the casual declaration of what amounted to complete sexual freedom within his own home.

"Everyone present has already agreed to these terms," Runeas continued relentlessly, as though discussing something as mundane as household chores or grocery shopping rather than complete restructuring of intimate boundaries that turned his home into something he'd never imagined. "This arrangement keeps you stabilised at a state where you can actually control your aura, prevents the kind of dangerous buildup that's been making everyone in this household absolutely miserable these past weeks—which would eventually start affecting the general public if you don't properly manage it. This isn't just about comfort, Shirou. It's about safety—for you, for us, for everyone."

"Though the kitchen," Lady Avalon interjected with delicate emphasis, amusement dancing in her ancient eyes as they sparkled with barely suppressed mirth, her voice light and teasing, "should probably be designated a safe zone. For sanitary reasons, if nothing else." All eyes swivelled simultaneously to focus on the two primary culprits, the weight of collective judgment making Shirou wish the floor would swallow him whole, his face burning hotter than the previously charred salmon.

Despite his overwhelming mortification—the embarrassment threatening to actually kill him where he sat, his naked state making him feel even more exposed under their scrutiny—Shirou found himself nodding rapidly in agreement, his head bobbing like a puppet on strings, the motion jerky and desperate as he grasped at any shred of propriety.

"Any guests who aren't participating in this arrangement or properly informed of the situation should be received at my mansion instead," Runeas added with practical efficiency, her tone shifting back to businesslike organisation that brooked no nonsense. "We'll maintain proper appearances there for official business and social obligations. This space—this home—is exclusively for those who understand and genuinely accept the situation."

"We should probably have the workshop spaces warded against the aura as well," Rin suggested, having apparently found her voice, her tone was matter-of-fact. However, colour still stained her cheeks in a way that betrayed her lingering embarrassment. "Can't have your aura interfering with delicate magical processes, corrupting experimental thaumaturgy, or be distracting in general. Though I'd wager the investment to ward something that way would be expensive."

"Yes, it's more the size of the lodestone we need to ward something like that. We'll add that for the other residences being constructed," Vivian confirmed with a thoughtful nod, her crystalline eyes gleaming with scholarly interest as she considered the logistical challenges. "Separate living quarters with proper protections."

The systematic way they'd planned everything—the careful consideration of every possible detail, every potential complication, from magical infrastructure to social appearances—made Shirou's head spin dizzyingly, the scope of their preparations hitting him like a physical blow that left him reeling. Whilst he'd been drowning in guilt and self-recrimination, flagellating himself for problems he couldn't control and isolating himself in misguided protection, they'd been efficiently constructing an entire infrastructure around managing his condition.

"This is..." He struggled desperately for adequate words, his voice rough from disuse and other activities he refused to think about right now, the sound scraping in his throat like gravel. "You've all... this is too much..."

"Done exactly what needed doing," Runeas finished firmly, cutting off his protests before they could properly form, her tone brooking no argument as sympathy and steel mingled in her ancient gaze. "Nothing more, nothing less. You're not alone in this, Shirou. So stop trying to be. Stop trying to shoulder everything yourself like some kind of martyr."

"So, Shirou," Lady Avalon said with a grin that was absolutely wicked, mischief dancing across her ageless features like starlight on water, her voice pitched to provoke maximum reaction as she leaned forward with gleeful anticipation, "what does it feel like to have your own free-use den of debauchery? Your own personal pleasure palace constructed with meticulous care?" Her tone was deliberately teasing, pitched to provoke exactly the flustered reaction she clearly anticipated, her ancient eyes sparkling with delight at his discomfort.

Shirou felt heat crawl up his neck despite everything, the embarrassment warring with grudging gratitude in his chest like two opposing currents, leaving him caught in the middle.

"Though," Vivian interjected smoothly before he could formulate any response, her expression shifting to something more businesslike yet no less intriguing, "before anything... else begins today, Lady Avalon and I have been gathering materials for a special project. Something you'll find particularly interesting, I suspect."

The knowing look the two women exchanged sent curiosity spiralling through Shirou's thoughts, momentarily displacing his lingering mortification with a spark of wary intrigue that cut through the overwhelming gratitude and guilt. Whatever they'd planned, whatever came next—he had the distinct impression his carefully ordered world was about to shift once more.

Though as the pair stood up with graceful synchrony, Lady Avalon was already gesturing for him to follow with that wicked, expectant grin that promised further chaos, Shirou found himself utterly unable, as his legs had fallen completely asleep from the extended seiza position, the punishment's physical toll catching up with him in the worst possible moment.

Pins and needles exploded through his calves and thighs in vicious, burning waves, the numb limbs refusing to respond to his desperate mental commands as blood rushed back in painful prickles, leaving him frozen in place like a statue caught mid-prayer, his face flushing anew with fresh embarrassment as everyone's attention turned back to him.

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End

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