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Story: [Illya vs Dementors]

Summary: Apartments in London are sparse and expensive, thin walls are a fact, and Rin is a woman with needs. Ergo, Illya gets sent to the first boarding-school that Rin can find.

Crossover: (Fate Stay Night) / (Harry Potter)

Genre: Humor

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Disclaimer: I don't own anything.

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The sound of crying, the sound of a woman screaming, a voice that-...

Harry blinked awake in a dark compartment, cold to the bone.

An inhuman screech in the distance, and the train shook underneath him.

"What the bloody hell was that?!" Ron's voice, and glancing over, Harry found him clutching his wand in a white-knuckled grip.

"Up until a moment ago, I would've answered 'Dementors', but they usually don't explode." The man they'd found sleeping in the compartment said, frowning heavily before glancing over at Harry and hurriedly digging through his robes to hand over a bar of chocolate. "Here. It helps with Dementor-exposure, at least."

"But Dementors aren't supposed to be away from Azkaban, right?" Hermione asked, sounding a little panicked.

Harry had never really heard about Dementors before, but if that's what they were like, Harry could understand why Hermione was panicking.

The sound of more screaming cut the conversation short, and the man quickly made his way out into the corridor. "You kids stay safe, I need to go check on the rest of your classmates."

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In hindsight, that was probably Harry's first encounter with Illyasviel von Einzbern.

The Dementors had boarded the train to make sure that Sirius Black wasn't on it, and a new student – a third year who'd transferred in from another country, or something, it seemed complicated – had used magic to blast apart a train-cart in retaliation.

She got detention for it, and she definitely became pretty much instantly infamous among the other students, but nobody seemed to really blame her for 'overreacting'.

No Dementor had really been harmed by the explosion, but the explosion had indeed driven them away temporarily, and apparently the Minister of Magic was in a bit of hot water for allowing Dementors so close to students without extreme safety-precautions.

Very specifically, it again seemed to have circled back to something about the complicated circumstances of Illyasviel von Einzbern's transfer into Hogwarts.

Something-something, very old isolationist family, something-something, impressions about the rest of the magical world if this is how they're greeted when they make an attempt to reach out, something-something, political suicide, something-something, rich enough to own several castles.

Harry didn't have the faintest clue how true any of those things were, and he wasn't really overly inclined to ask the girl in question about it either. He was just going to enjoy not being the center of attention for once. It was very novel.

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Illyasviel von Einzbern was an international incident waiting to happen, Albus had known that since Rin Tohsaka had first contacted him about the possibility of allowing her entry into Hogwarts.

The Einzberns had been locked away in their isolated castles since before the Founding of Hogwarts. An ancient kind of bloodline, only venturing outside during extraordinary circumstances, which very rarely seem to coincide with whatever was happening in the wizarding-world.

No, despite being a deeply rooted German family – though Albus wasn't sure if they technically considered themselves as such, considering how much older they were than the actual country – the Einzberns were wholeheartedly magi.

A magi-stronghold – outside of the Clock Tower and its heavily-disputed role as an embassy – would've never been allowed within Europe's borders. But they'd been around since before the invention of wands, before that invention had been classified as a state-secret, before the British and their neighbors used their new tool of magic to wreak havoc on established countries through 'colonization', and long before the magical countries outside of Europe had unanimously closed ranks against the European magical countries in retaliation.

There'd been a great many wars fought over the secrets of the wand, but that particular argument had long since fallen by the wayside. If Albus were to guess, teaching your children how to use a wand gave them a great ability to perform things that they would've never succeeded at without them, at the loss of a rather important piece of magical understanding that Albus had never quite managed to track down.

There was a reason that the Ministries of Europe had banned nearly every single magical ritual ever invented, and it had a lot less to do with regulation than it had to do with an immense death-toll. Older families could throw a fit about 'traditions', but when those same traditions killed more than half of the people undergoing them? No, they very much needed to be carefully regulated or banned.

The fact that the rituals seemed to have a nearly perfect odds of the participants remaining alive, as long as it was done by magi? That had sparked a new wave of wars, with older families demanding that they 'return their magic' or something like it.

To Albus, the obvious answer was simply that the magi had learned to do something that allowed them to actually understand why rituals did what they did, thus allowing them to actually make sure that they were used as the tools they'd been designed to be.

Not that either side had really made any progress with understanding how the opposite side actually did their magic. Wands were too complex for the magi to decipher properly, and rituals were too alien for wizards to interpret.

Albus had never been particularly fond of how the magi had so greedily refused to share those abilities with the wizarding-world, but then he didn't really approve of how the wizards had greedily kept the secrets of the wand from falling into the hands of magi, either.

Both sides were at fault, and both sides had their issues.

A magus might be able to perform rituals without worry, but they were also infinitely more limited in how that magic took shape than even the most squib-like wizard. But of course, whether you boiled someone's blood or cut off their head, at the end of the day, they were equally dead.

Albus had honestly never even tried to count how many times the different sides had descended into war over something or another. It'd been so frequent that after a while it seemed to have more to do with the simple fact that both of them loathed everything the opposing side stood for, rather than any desire to learn their greedily hoarded magic.

That had been why the Clock Tower was founded, in the end.

A place away from Europe's borders – where everyone could still freshly remember the blood spilled – and in a trade-hub where a great many strange people arriving through muggle-transportation wouldn't be seen as unusual.

Magical travel would've probably been as heavily regulated as wands, if it hadn't been for how someone would have to decipher wands before they ever stood a chance to unravel what someone had actually created with a wand.

So yes, the idea of Illyasviel von Einzbern – a magi to the core, despite her homeland – being allowed within Hogwarts' walls, was very much an international incident waiting to happen.

Albus didn't regret agreeing though.

Ignoring how a contact with the magi might finally give them an upper hand against Voldemort, Albus was quite frankly sick and tired of the divide.

The colonization was bad, nobody was going to argue about that. They'd done some horrible things, things that they very much couldn't blame on the muggles. But Albus knew perfectly well that muggles had started to move between countries, even outside of their former colonies, and they'd be running into an international incident sooner or later regardless.

Say that a Chinese family of muggles settled down in Britain, only to have a muggleborn child? Oh, they might be able to dodge it by claiming that the child's family came from Hong-Kong and that she was as such part of the wizarding-world, but that would only hold up for as long as those countries were willing to look the other way about it.

The moment a country decided that Europe was 'stealing' their muggleborn through muggle-emigration? Or that Europe decided that the magi were doing the same? That was very much a war waiting to happen.

Sooner or later, they needed to bridge that gap that everyone seemed so insistent on widening. And though this particular way of doing so might be reckless to the extreme, Albus couldn't regret agreeing to it when it was offered to him.

Illyasviel von Einzbern was just enough of a figure in the wizarding-world to slip through the cracks, to keep politicians from looking too deeply into her magi-like roots. And Albus was a firm believer that if someone offered you a hand in peace, you took it.

Perhaps you needed to check for contact-poison on the hand, and perhaps you should keep ready in case a hidden weapon tried to stab you, but you took that hand. Sometimes that didn't work out as well as he wanted it to, but that didn't mean he could allow himself to stop trying.

Kindness could break down many a door, which anger and suspicion had kept solidly closed.

Though, Albus was still rather curious about what exactly Rin Tohsaka had gained by approaching him with the suggestion.

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The Holy Grail Ritual War didn't so much need volunteers as it needed convenient victims.

Seven magi all unknowingly branded with a mark that was designed to bind them to the ritual in death, fighting to the death over who was to be allowed to leave the ritual alive.

Oh, there was a price for the winner, but it was very much a struggle of survival more than anything. And of course, as with any life-or-death struggle where a price could be found by the survivor, everyone cheated.

Whether it be alliances with people uninformed of the nature of the ritual, promising to spare their lives, when in reality you were simply going to kill them when they lowered their guard. Or bringing in outside magi to help with murdering their fellows.

In the end, for every attempt at the ritual, none had been successful in the end. There'd been survivors, several of them in fact, but none had ever been able to claim their price in the end. After all, whilst cheating was the only viable way to win, it was also something which broke and twisted the rules of the ritual to the point where the price would never manifest.

And so there was no desire to ever participate in the useless ritual, and yet it kept claiming victims.

There were no more Matou, the entire family killed to the last. Sakura might still own the name, but she'd always been Tohsaka by blood. Kotomine was dead too, and the bastard priest had very much deserved every moment of it.

There'd been an actual seventh magus as well, but Kotomine had likely taken care of that as part of his way to steal another chance at the 'grand price' for himself. He might've been part of the previous war, and he might still have had the brand on his skin, but the ritual only accounted for seven magi, and with Kotomine they would've been eight.

Zouken hadn't so much joined the actual ritual, as he'd set out to murder his adoptive granddaughter. Which was only to be expected, considering how she'd ruined all of his plans to make use of her when her own participation in the ritual didn't exclude Shinji from being chosen as well. That Sakura then also murdered her adoptive brother – rather than protect him with her dying breath – in retaliation for the treatment she'd suffered at his hands over the years, just made it all the more obvious that Zouken had reason for his grudge.

Shinji, Sakura, Rin, Shirou, an unknown mage dead by Kotomine's hands, a nameless magus going by the call-sign 'Medea', and Illyasviel. That had been the full list of participants in the fifth Holy Grail Ritual War.

In the aftermath, only four magi had been left standing. Mainly because none of the remaining participants actually cared overly much about the 'grand price' of the ritual. Rin might've considered murdering all of them anyway, but she didn't really want to tangle with Illyasviel and Sakura in an all-out fight, and murdering Shirou was a bit like kicking a puppy.

Also, Shirou without a shirt on was-... It'd be cruel to deny the world that kind of view. Even if Sakura's own very obvious interest in it made for some... awkward situations.

Rin didn't entirely mind though. Sakura didn't either. And perhaps-... Perhaps the two of them weren't entirely-...

Basically, the threesomes had stopped being awkward halfway through the first one, and had probably only gotten raunchier and more enthusiastic since.

And, as the older sister, who'd grown up in a proper household rather than as some weird sister-slave, Rin felt like she should really feel a lot more guilty about that than she did.

No, in truth, by the time Rin realized that trying to keep her own magical research afloat on an economical level was doomed to failure – unless she found herself a well-paid job of staring into a wall somewhere – the three of them had already ended up joined at the hips.

After that, Rin – being the only one with the ability to both plan ahead, and in possession of any amount of common sense – started pulling strings. Strings that would hopefully end with the dismantling of the system surrounding the Holy Grail Ritual War, and would until that point get them all the hell out of the country, and into a place where Rin could do her research in peace.

Enter, the Clock Tower.

It was a political entity that no magi wanted to touch with a stick. It was also a political position that nobody they were supposed to be making friends with wanted to touch with a stick, either. In other words, the work-environment was isolated and completely inane.

Which meant that it was absolutely perfect for Rin's goals.

Except for one thing. The Clock Tower was one building, and cheap living-arrangements in the middle of London weren't exactly easy to come by, which meant that they'd have to share an apartment.

No problem. In fact, grand success. Rin had no complaints whatsoever to sharing living-space with Sakura and Shirou.

The problem was Illyasviel, who of course refused to leave Shirou alone for any longer period of time, because the little brat had abandonment-issues that were as bad as Sakura's. And Rin very clearly drew the line in the sand in regards to her debauchery in inviting a barely-teenager into a foursome, with the girl's own adoptive brother.

She thankfully wasn't alone in that, and Illyasviel didn't seem to have any interest in that kind of arrangement in the first place. But living in a small apartment together?

Rin was a woman with needs, and she'd prefer that none of those needs led her down the slippery slope of exhibitionism. So Illyasviel needed to go.

Now, obviously, Rin couldn't just kick Illyasviel out anymore than she could rent a second apartment. Which meant that she needed to convince the little brat that there was a big and exciting world out there for her to explore, and that she should get on with exploring that for massive amounts of time, very far away.

Enter, Hogwarts and the Wizarding World.

As far removed from magi as the magical world was from the non-magical one, the Wizarding World was perfect for distracting an easily excitable brat. The fact that it also included a school where Illyasviel could interact with kids her own age – who were less horrifically traumatized into murderous rampages, and generally less magi-like in their ideological values – just made it easier to sell to Shirou.

Illyasviel had opinions, but she was a kid, and Rin knew a lot of her weaknesses at this point. One of them being the fact that Illyasviel really didn't want to be walking in on their threesomes any more than she already had.

Once that was over with, Rin just needed to sell the idea to the politicians and the headmaster of Hogwarts, and what do you know? They bought it, hook line and sinker.

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"She blew up the train?" Rin winced inwardly, already imagining what that would cost if they got stuck paying for damages.

Still, she wasn't really surprised. Rin really couldn't imagine a good reason to have Dementors around a school, other than if you had a sudden desire to horrifically traumatize and kill most of the student populace.

In light of that, being by all accounts attacked by Dementors – the students should've been informed of the Dementors planning to stop the train, unless they'd decided to do so completely on their own initiative – and reacting with violence was hardly surprising.

No, Illyasviel might've blown up the train, and Rin might be wincing at the potential price-tag of that, but she couldn't fault the girl from trying to defend herself. Dementors were hard to hurt, let alone kill, so trying to drive them back was very much the kind of thing that a magi might expect to result in collateral damage.

Wizards might not be of the same opinion, what with some of their spells being uniquely suited for the task of driving them away, but even those spells were pretty high-end on their curriculum – as far as Rin understood it, anyway.

"Indeed, she did." The headmaster's eyes twinkled with what might very well be merriment. "The Dementors had no place on the train, which is why I asked our new Defense Against Dark Arts professors to escort it. I understand perfectly well that the unfortunate damage to the Hogwarts Express wasn't intentional on young Miss Einzbern's part. They're very unpleasant creatures, and I can hardly fault my students for attempting to defend themselves."

The Minister was wringing his hat in his hands, looking both very nervous, and very much like he didn't agree. Considering that Cornelius Fudge was apparently the one who'd originally placed Dementors around the school, and that he'd been rather vocal about Illyasviel burst of 'unprovoked violence'?

The Minister of Magic might be a spineless kind of man, but he was also clearly aware that he was outvoted, and that he technically didn't have any authority to voice any real opinion on the matter. The Hogwarts Express belonged to the headmaster, so damage that it'd suffered was up to the headmaster to demand reparations for, and the Dementors had all escaped unharmed, so the Minister couldn't demand anything for that.

It was kind of disturbing to find a politician who was more interested in stroking their own ego, rather than blackmailing and backstabbing their way to ever-more power. Rin was admittedly only in it for the salary and the relative privacy of being a politician in a position nobody wanted to talk to, but that was Rin.

She was under no illusions that she was probably as messed-up emotionally as the rest of the survivors of the Holy Grail Ritual War. Shirou with his suffocating guilt at being alive whilst others weren't, Sakura with her hatred-guilt-despair-bitterness-cruelty over basically every emotional attachment that she'd ever had, Illyasviel with her abandonment-issues and willingness to murder everyone who considered leaving her, and Rin.

Rin's issues stemmed mainly from an inability to let people come close to her, and control-issues, with a bit of a temper and a willingness to consider murder and theft to be reasonable solutions to someone shortchanging her. Also, she clearly had some weird sexual kinks that she wasn't even going to try to figure out.

Regardless, Cornelius Fudge was an unpleasant kind of individual, and Rin would've felt a lot better if she was allowed to just squash him like a bug and have Lucius Malfoy elected in his place. At least with Malfoy, you knew that he was a narcissistic sociopath with too much money and ambition, and far too little ability to back up his big mouth.

Playing the political game with Malfoy at least made sense. Fudge always left her feeling as if she'd stepped in something nasty, except it'd immediately disappeared before she could scrape it off, and now she wasn't sure if she was just imagining it.

Albus Dumbledore was a more pleasant person to deal with. Sneaky and manipulative, and probably collecting as much blackmail-material as he could fit in his gigantic beard, but very much a man with a long-term plan. A long-term plan that required a lot of players to remain on the board, and a genuine belief that diplomacy was preferable to forcing one's hand.

Rin trusted him about as far as she could throw him, but that had less to do with the man, and a lot more to do with Rin not trusting easily. Kotomine had always been a creep, and she'd have happily murdered him in his sleep if she'd thought that she could get away with it, long before he'd ever tried to murder her – or she'd found out about who exactly was responsible for her being an orphan.

Dumbledore very much didn't give off the same feeling of 'creepiness', but then you didn't need to be a murderous maniac to screw someone over.

And she still was pretty damn sure that the headmaster had a plan for why he'd let Illyasviel join his school. A plan that was a lot more complicated than the Minister's ignorant belief that the Einzbern family was simply a very old wizarding-family with deep pockets.

Rin desperately wished she could sell-off all of the Einzbern's castles, and then simply live off of that for the rest of her life. But even if she could manage to convince Illyasviel of doing that, Rin still had her future descendants to think of, and so long-term investments was the name of the game.

Rin nodded along to Dumbledore's words, continuing to politely ignore Fudge's unspoken opinion. "I will ask her to try to limit the collateral damage in the future, of course. But avoiding such would perhaps be easier if she had some real way of defending herself against them, should she feel threatened in the future?"

For one single moment Rin suddenly realized Dumbledore's whole reason for being so willing to sweep the incident under the rug. The way his eyes had lit up, as if she'd played right into his hands, before being tempered into the regular twinkle of eccentric merriment.

"There is a spell for it, yes. A little bit advanced for children, according to the Board of Governors, but in these circumstances I'm sure it will help to reassure more students than just Miss Einzbern." Dumbledore said, grandfatherly smile on his face.

Illyasviel's incident with the train was being used to leverage anti-Dementor spells into the curriculum, against the previous wishes of the Board of Governors? Rin could work with that.

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A/n: This setting is... complicated and old. I've been wanting to use it on a fic for ages upon ages. A fusion between Nasuverse and Potterverse, where the thing separating magi and wizards are the wands that wizards long ago created, and then fought bitterly to monopolize, only to end up forgetting how magic that didn't rely on a wand worked.

The Holy Grail War didn't include summoning Heroes from the Throne, and was instead relegated into "magi endlessly murdering each other by hiring mercenaries when they were supposed to perform a magical ritual with their battle". Basically, a useless kind of ritual that claimed a hell of a lot of lives.

(Zouken's plan for buying Sakura from the Tohsaka was "she'll be the Matou-family sacrifice to the ritual, and if she dies, boohoo, and if she wins I can have her properly marry into the family afterwards, win-win". Except obviously Sakura loathed them both and murdered them rather than be sacrificed by them, thus forever ending the faltering Matou-line.)