This is written with the Exolvo headcanons in mind, a Harry Potter and Frozen crossover started by ultranos, arendellesfirstwinter and counterpunches on Tumblr. Check out the Exolvo tag, there's a Timeline/Masterpost that should easily help you get started. Lots of good reading and fun ideas.

Enjoy!

Four Houses

It's a game.

It's a challenge, a distraction.

It's the perfect diversion for a nervous young first-year, out of her comfort zone and fighting to keep the ice in whenever someone talks to her out of the blue.

"Hey, Arendelle!"

She bites back the taste of frost, stills her beating heart and looks, desperately, for clues. The gloves help. Papa was right. Papa is always right. Suddenly the paintings on the walls come into sharp focus. She finds herself counting bricks, memorizing the angle of an arch, reading the names off plaques and trophies alike. She's looking, always looking, and it helps. The ice recedes. She turns to face her fellow student.

"..."

The fear is still there, but restrained. She nods, recognizes them as one of the Slytherin prefects, a girl with long black hair. She doesn't frown or flinch when she grabs her shoulder, though her gaze grows sharper with the pounding in her ears.

"You lost your way to the common room again?" The older girl relinquishes her grip on the first year. Elsa thanks the gods that not many of her House appear to be all that touchy-feely. She shudders at the thought that Hufflepuff was ever a possibility. The first years wearing yellow and black always seem to be getting tackled into hugs by their peers. Finally acknowledging the prefect's question, she merely shrugs.

She doesn't need to know what she is doing out here anyway.

"Come on, this way Arendelle. You do remember the password, don't you?"

"Clever fox." She whispers, loud enough for the girl to hear.

The brunette smirks, giving the small blonde an appraising glance.

"There's hope for you yet, Arendelle." And she points her down the right corridor, towards the wall of brick and stone in the dungeons that houses their common room, before returning to her patrol... She's probably off to find more lost first-years to redirect. Elsa sighs.

This game is going to take a while.

As she settles into her new routine, Elsa slowly adjusts. She's more prepared now, when other students accost her. She's more confident, now that she's started to earn some respect from her fellow first years, if only for being able to keep up with all of the information they're being overloaded with in class... The hours in the library certainly help her to answer their teachers' questions correctly. She's spent plenty an evening practicing the wand motions they've been shown.

The game has been put onto the backburner for a while. She finds that she's enjoying all the challenges Hogwarts throws at her. Elsa's enjoying the freedom, the magic, and the chance to observe others without fear of her sister getting in harm's way...

Not that her wandless magic has stopped being a problem, far from it. It's still the longest she's been away from home, from her family. There are nights where her homesick mind will struggle, and she begins hearing things... She hears her sister's voice at a door that isn't even there. She hears her father calling for the two of them, her mother stating that dinner is ready. These are the nights where her imagination runs wild, her heart is amok and she finds herself slipping out of the dungeons, exploring the castle past curfew, playing the game because it is the only thing that keeps her ice from spilling out, her thoughts from going back to that fateful night, three years prior, where her parents had sounded so fearful, where Anna had gone so dreadfully quiet.

"There are four houses in Hogwarts," she remembers her father telling them, as Anna had excitedly asked for the hundredth time for more details. Elsa's younger sibling had wanted to know everything there was to know about the school from the moment the letter had arrived. "Gryffindor, Hufflepuff, Ravenclaw and Slytherin..."

She whispers the names to herself as she wanders past chainmail suits and abandoned portraits, barely stopping in time to hide the moment she spots Peeves out the corner of her eye. The last time she'd been caught out late by the poltergeist had been particularly unpleasant. She didn't like him. He was too unpredictable... too keen to poke at open wounds. If the Bloody Baron hadn't distracted him, Elsa couldn't bear the thought of what might've happened... and she still isn't certain what to think of the Slytherin ghost.

"What houses were you in, Mama, Papa?" She recalls an excitable Anna bouncing as the family walked down Diagon Alley, Mama thankfully keeping the small red head on a tight leash as Elsa clung to their father's robes. Elsa remembers how fearless her sister had been as they'd visited the pet-shop, cooing and awing at adorable kittens, slimy toads and fearsome owls alike. Elsa had been particularly intimidated by a large beast of an owl, icy blue eyes glowering at them as its white plumage puffed out into sharp looking spikes of feather and claw.

Anna had named it Marshmallow.

It was then that Elsa knew, without a shadow of a doubt, that Anna would fall into Gryffindor, "the House of the Brave and Daring." Only Anna could have such a knack for making the scary look cute, the threatening look small.

Mama and Papa had exchanged a glance and a smile then.

"Why don't we make a game of it?" Papa had offered, his warm hand catching Elsa's shoulder in a protective touch. "When you're at Hogwarts, look for clues. There should be quite a few, and write to let us know which House you think we were in."

"Oh! Oh! And tell us which House you are in!" Her little sister chirped; the eight-year old beaming at her. "I bet it'll be Ravenclaw. You're so smart."

"What do you think, Elsa?" Her mother's quiet voice startled Elsa out of her thoughts.

"I..." Oh yeah, she hadn't replied to her father's suggestion. She gave her parents a small smile, feeling warm at the idea of learning more about their time in Hogwarts while there. "Sure, sounds fun."

And now, homesick and sad, walking through the empty corridors, she is calling upon the game to help her forget the pain, to help her feel the warmth she misses. She isn't the only one who longs for home. Some of the other first years have been talking about parents and siblings with a tear in their eye. Others try to cover it up under boastful claims. One boy, Draco Malfoy she thinks his name is, had gone on at length about how his family was full of Slytherins as far back as they could remember, how that meant he was a pure Slytherin, through and through. An older boy who'd been in the common room at the time had openly scoffed, before plastering on a sickly smile.

"Sure you are." She recalls he said his name was Hans.

Elsa decides that she doesn't like the two of them very much. They are abrasive and challenging and make her miss home all the more. They make her miss Anna.

Elsa always misses Anna.

So she distracts herself with thoughts of Mama and Papa and tries to figure out the best place to look for clues as to the houses they had belonged to. It strikes her as she hides behind a curtain, holding her breath as two professors walk passed, talking about the year's inter-house Quidditch cup.

Yes, she decides, the Trophy room would be a good place to start.

It turns out Agdar Arendelle was keeper for Ravenclaw during his time at Hogwarts. His name is on the trophy, along with several others, for the year that, she believes, would have been his fourth year.

No sign of an Idun though.

Nevertheless, she writes, as promised, with the answer she has found so far. She keeps things simple, straight-forward, not wanting any of her fears or doubts to reach them through the letter she sends. She isn't expecting the reply as soon as it comes, but she can't help but smile as it does.

Marshmallow swoops in, wings wide and powerful with the flock of delivery owls at breakfast. She only notices because of the screams of some fellow first years as the great white accidently bats their heads with his feathered tips. He lands heavily in the middle of the table, upending some of the serving bowls and their contents. He drops the envelope in front of her before turning to shriek loudly at one of her neighbours who'd seemed a bit too curious. She takes a moment to shake herself out of her startled daze. Finally she distracts him from glaring at a rather scruffy smaller owl two seats down by stroking down the raised feathers upon his back. Instantly he halves in size, great ice blue eyes turning to gaze at hers, the sharp blue-gray spiked feathers now hiding amongst the softer white ones. In the short month since he has become her owl, she has learnt to know him. Not the smartest of owls, but loyal and protective to a fault.

"Thank you, Marshmallow," she says with a smile, offering him a chocolate treat. He takes it with a short hoot, appreciation she thinks, before flying back out, much to her neighbour's relief.

"That thing's huge!" The girl says. Elsa holds back a chuckle at her fellow's nervousness. That had been, after all, her same reaction when her family had visited the owl emporium he came from.

Looking at the letter Marshmallow delivered, she hesitates. She recognizes her father's angular handwriting, the crisp way he tilts his Es as he writes her name. She had only sent her letter two days ago, she hadn't expected a reply so soon...

But then happiness and curiosity win over and she tears open the envelope, only waiting a moment for her neighbour to return to her breakfast before unfolding the parchment inside.

... we cannot hide our surprise at hearing you are in Slytherin! Anna was...

Her hands snap the letter back into its folded state. Her breath catches as she feels the cold shiver along her spine. No, she cannot read it here. She has been so focussed on her father's game that she forgot to consider what they might think of her being assigned to the house of Salazar. She's not ready to face their words on the subject, not now, not here. Discreetly she slips the letter into a pocket of her robes, to peruse later in a safer location. Her blue eyes scowl, unseeing, over her plate.

The chocolate tastes bitter this morning.

Dear Elsa,

We are very glad to hear that you are settling in fine at Hogwarts. Papa's ever so glad that you are enjoying your classes, and he's been showing off the early grades you sent to all who'll listen. Typical of a Ravenclaw, as you correctly deduced. We had somehow forgotten his house had won the Quidditch cup that year. Thank you for sending us such a lovely reminder of that time, dear. I can still see the stitches he needed on his upper lip after dodging the worst of a nasty Bludger blow, not that he let that cut stop him from celebrating first!

He hasn't helped but notice that you haven't figured out what house I was in yet. I'm not too worried: I know you will figure it out. You've only been there a month after all. Take your time.

Speaking of houses, we cannot hide our surprise at hearing you are in Slytherin! Anna was so stunned at the news that she dropped her breakfast onto her kitten. Thankfully, Olaf never seems fazed by anything, and Anna soon bounced back with more questions, as per her usual.

You haven't told us much about your classmates. I hope you are managing to make some friends. The friendships you'll make at Hogwarts will stay with you for life. Papa and I both know your smarts and kindness will help you find like-minded people.

We're all doing fine. Papa's busy as always at the ministry, and I swear the piles of paperwork he brings home to finish off keep getting bigger. I'm still doing the odd stint at Saint Mungo's, helping out when my health allows, which thankfully is often these days. Anna misses you, but is keeping busy as usual. She somehow managed to get a bike all the way to the second floor without us noticing yesterday. I will never know how your sister manages to get away from such stints with nary a scratch, but she did.

Please keep in touch. We very much look forward to hearing from you again. You have always made us proud.

Lots of love,

Mama, Papa, Anna + Olaf.

It's her mother who writes, Idun's writing as flowery as the rosemaling she likes to decorate their home with. She feels a flush of pride as her deduction with regards to her father's house is proven correct. Though she still lets out an unfortunate burst of frost upon reading their reaction to her being in Slytherin, she is very relieved to find no negativity there. She finds herself shedding a tear upon reading of her sister's antics. She crumples the paper against her chest, feeling the warmth radiating from the words upon it, from the adorable scribble Anna drew under Olaf's name of a paw print to the loving advice and pride of her parents. She feels a wave of homesickness take over, making her head spin and throat choke, yet there's also a nugget of something new spreading through her.

She feels a new confidence dawning.

Elsa had asked the hat to sort her into Slytherin. Elsa had thought the house would be full of ambitious and cold-hearted elitists, to put it simply. It hadn't been a total misconception, she's certainly seen many a Slytherin who seem to fit into that mould... but she has also seen others who don't. Not just her, she's seen first years in green who are shy and hesitant, third years who show warmth and patience, sixth years who frequently hang out with Ravenclaw or Hufflepuff students. Though the established preconception of Slytherin seems to describe most of its members, she's now seen enough to know that her house has another, hidden, less dark side just waiting to shine.

And she wants to help her house shine.

Wiping away the last of her tears, she quietly exits her cubicle with a small wince. She's leaving considerably more ice behind than she would like, but she's never figured out a way to make it melt away.

"Sorry," she whispers to the resident ghost. Moaning Myrtle just glares at her, sobbing getting in the way of whatever she had been away to say. Not wanting to disturb the spectre any further, Elsa leaves. She feels a little sheepish about using the haunted lavatory as a place to hide away, but resolves to try and visit the ghost again at some point... After all, Moaning Myrtle doesn't seem all that bad.

She pauses on her way to her next class, spotting a lost looking first year with a red tie, the boy's ginger locks reminding her of her sister's.

"Hey," she asks, barely managing to project her voice. "Are you looking for the potions class?"

"Er, ah, yeah..." He stutters, his brow curving into a confused frown as he notices the colour of her tie.

She feels the warmth from the letter in her robe's pocket once more. She wants to fight against her house's reputation. She wants to help people, no matter where the sorting hat put them. She wants to make her parents proud.

"It's this way." She says, leading the lost boy down the right corridor. She doesn't expect him to trust her, but she is glad to see him follow, even if hesitantly at first.

The relief on the boy's face as he spots his classmates warms her heart further. She doesn't expect any thanks as he skips to their side, leaving her behind with her fellow Slytherin.

"Cheers for that!"

She gets it anyway. The Gryffindor student's gratitude is enough to help her through the most challenging of her classes, a smile on her face.

That night she finds she manages to sleep without a pang of homesickness.

"Thank you, Mama..."

The month of October is spent, between studying, classes and flying broom lessons, setting about her new resolution and trying to complete the second half of the game. Idun's student House is proving a lot harder to track down.

She's perused all the trophies in the Trophy room, all the student pictures in the various corridors and a good sample of student essays in the library before she thinks to search for her mother's surname. It takes her moment to consider. Idun wasn't always an Arendelle. What is it Gran-Papa calls himself... Papa North? Yes, that was it. Idun's maiden name was North.

Using her mother's maiden name certainly opened up her research options, many a plaque or group essay merely marked with a student's first initial followed by their surname. It turns out, however, that the surname North is a lot more common than Arendelle throughout Hogwarts recent history, and soon Elsa is recording varying instances of ' ' without getting any closer to her goal.

The blonde sighs as she scribbles various notes in her small notebook, quill neatly dividing each instance of the name into the four houses they were associated with. She had been hoping to have the puzzle solved by Hallow's eve, but there she is, sat at her house's table during the Hallowe'en Feast, no closer to her goal than she had been at the start of the month.

"What you doing?" A voice sings next to her.

Out of sheer reflex, she snaps the book shut. Warily looking up to the Slytherin first year sat next to her, she weakly answers.

"It's nothing."

"Doesn't look like nothing," the girl, a brunette named Sylvia leans closer, causing Elsa to lean back. "Relax Arendelle, I won't bite. I'm just really curious what's got you looking so down when we're surrounded by this!"

The girl waves her hands around them, indicating the vast feast, mesmerizing décor and spooky entertainers. All the other students seem enthused, but Elsa finds she just isn't in the mood for it.

"Just worrying over that last potions lesson, is all." She lies, though there is a degree of truth in it. Professor Snape has made it no secret that he is unimpressed by her inability to control her cauldron's fire adequately.

"Snape's just a sour face..." Sylvia pulls a face to illustrate, managing to draw out a small smile from the blonde. "Tell you what, if we team up next time, I'm sure I can help you out with the brewing."

Surprised by Sylvia's generous offer, Elsa finds herself nodding before she gets a chance to think it through.

"Sure..." She quickly slips her notebook and quill away, before pulling her gloves on tighter, the pull of leather helping her still the nervousness in her limbs. "I mean, yes, please. I... I'll be more than happy to do all the chopping and measuring in exchange."

"You got a deal, then." The brunette grins, holding out her hand.

Elsa is saved the awkwardness of actually shaking hands by a commotion at the entrance to the feasting hall.

"What's going on?" An older boy down the table stands the better to see. He needn't have, as the sight of Professor Quirrell barging into the room is unmissable.

"T-troll..!" The Defense against the Dark Arts teacher breathes the word shakily, before finding his voice. "Troll... in the Dungeons! Troll in the Dungeons!"

Elsa joins Sylvia in standing up, along with the rest of the Slytherin table and room to hear if the normally timid professor has any more to say. What little he has already shouted out to the room at large has been enough to cut out the music that was playing and put a stop to many of the raucous conversations that were going on before his dramatic entrance.

"Thought you ought to know..." The pale man then says politely, his focus upon the teachers' table at the head of the hall. That seems to be all the nervous teacher can manage, because that is when they see his purple turban sink down to the floor with the rest of him. Professor Quirrell just fainted, again.

Throughout the pandemonium that seems to grip the hall, Elsa is suddenly astutely aware of how terrified some of her fellow students seem to be at this news. More specifically, Sylvia is trembling like a leaf, and the blonde can feel her own blood turn cold with dread. Yet somehow seeing Sylvia turn whiter than a sheet hardens her resolve, stills the fear coursing through her veins.

"Sylvia?" She asks, tentatively. "Are you alright?"

"My..." The brunette gulps audibly, her eyes wide as her breath quickens. "My uncle was killed by a troll. I..."

Forcing herself to grab the girl's arm, despite the hum of cold inside her gloves and the sharp taste of winter in her mouth, Elsa gives her a shake.

"Hey, listen, it's going to be alright." Nodding towards the teachers' table, she adds with more confidence than she feels. "Look, the teachers are all going to find the troll. They'll know how to subdue it. They'll outnumber it easily."

In her panic, Sylvia hasn't noticed Professor Dumbledore issuing orders. Though the bulk of the students seem to have returned to an uneasy state of wariness, the brunette is still struggling not to run from the room. Elsa's grip tightens.

"Breathe deep," she says, remembering her father's advice during her worse bouts of panic. She tries not to think too hard on the burst of frost that had accompanied those words back then. Instead she forces herself to keep direct eye contact with the brunette. Cold blue eyes bore into dark green. "Don't feel it..."

"What..?" The brunette's breathing has slowed down, but there's still a hint of shallowness in her voice.

"Your fear," Elsa clarifies. "Don't let it show."

"Alright, everyone listen up!" A new voice shouts out, one of the prefects. Elsa recognises it as the prefect who'd caught her exploring back at the start of term. "Professor Dumbledore has requested that everyone return to their common rooms in an orderly fashion."

A shrill squeak makes its way out of Sylvia's throat, making Elsa jump. The blonde's hands are cradled against her breast as she in turn takes a deep breath, silently praying that no one notices the sudden layer of ice underfoot. Thankfully in all the commotion, people seem to assume it is but spilt drink.

"...But our common room is in the dungeons." Sylvia's voice comes out low but hoarse.

"Everyone line up; first years, to me!"

"It'll be alright," Elsa says, her voice sounding sharper than she'd like. "The teachers are headed down there ahead of us."

As she grips her gloves tighter and watches Sylvia line up beside her, she desperately hopes that what she says will hold true.

"Ouch!"

"Hush, this will be but a minute." Madam Pomfrey's voice is sharp, but not without consideration. As she applies the cream to the sharp bruises on Elsa's arm, the blonde girl biting her lip, the Matron tuts. "Honestly, what were you girls thinking..."

Elsa's cheeks colour as the older woman pulls her sleeve up higher, exposing a dark gash on her shoulder. If it hadn't been for her wandless ice magic, Elsa's not certain she would even have an arm left. Desperate to distract herself from memories of the troll barging past them, its club smashing the ice that in her fright Elsa had summoned as a shield, she forces herself to think of anything to distract the school nurse from asking any further on the matter. Her nerves just can't take it just now.

"Will Sylvia be okay?"

Elsa is surprised by the earnestness in her voice. She hadn't intended to be so protective of the girl, yet she can't help but feel this is somehow her fault.

Madam Pomfrey eyes her with a steely gaze, an emotion upon her face that seems to have little to do with healing.

"You're Idun's girl, aren't you?" There is unexpected warmth in the matron's voice, a small smile making its way onto the old nurse's face. "You're just like her, worrying about others before yourself."

"Wha-?" The blonde girl's surprise is cut short with a hiss, as the cut on her arm painfully squeezes shut. "You know my mother?"

"I don't know why I didn't notice it earlier: you look exactly like her, have the same face." The nurse hums happily as she pulls the girl's sleeve back down, much to the small blonde's relief. The relief is short lived however, the matron's hands reaching for Elsa's glove. "Now let's see your hand."

"No!" Clasping her hand behind her, Elsa is glad of the matron's care. She no longer feels agony in moving her arm, the cuts and bruises now feeling little more than phantom pain. Now if only she would stop touching her... Realising that her reaction appears to have startled the woman, she winces apologetically. "No, sorry, my... My hand's completely fine. Honestly."

The steel grey of the nurse's eyes bores into her once more, clearly looking for the first hint of a lie.

"Madam Pomfrey..." The blonde Slytherin is unable to hide the whine in her voice.

The nurse sighs and leans back, relenting. As she begins putting her supplies away she begins to answer Elsa's queries.

"Young Sylvia will be fine. She just needs a little rest. You can come visit her in the morning if you must." The brunette is lying in a bed a few feet away, sleeping off the fright of their encounter with the troll. She'd fainted at the first sight of it; much to Elsa's mixed relief after the beast had smashed through her ice and sent her to the ground. It was professor Snape who'd found them before running off, his voice sneering out at someone to get these lost Slytherin to Madam Pomfrey as soon as. Elsa is still a little shaken that it was Jeeves who answered their head teacher's call with much jeering.

The matron hands Elsa a damp cloth with which to clean herself up further, having clearly noticed the blonde's reluctance to being touched.

"As for your mother, I was already in charge here when she was a student. Idun was known for being a bit poorly, but she always worried about others first, to the point of self-neglect at times..." Madam Pomfrey smiled warmly at Elsa. "You really do remind me a lot of her. How is she?"

"Eh, ah... Very well thank you." The blonde was still startled that the nurse had known her mother at all, let alone that she somehow reminded her of her mother. A shaky hesitant thought made its way to her mind. "Tell me, Madam Pomfrey, please..."

"Yes dear?" The old nurse prompted. Elsa took another moment before finally asking the question, knuckles whitening beneath her gloves as she wrung the cloth tight.

"What house was my mother in?"

In the two months since she'd started school at Hogwarts, Elsa had always thought it would be cheating to outright ask someone. It is why she keeps the game a secret, hiding her notebook when any eyes look too closely, sneaking out at night to look for clues, asking for various essays under the pretence of study... Yet sat here in the infirmary with an old witch who clearly speaks of Idun fondly, Elsa can't help but remember her mother's advice to make friends and wonder if maybe that had been a clue.

"Why she was in Hufflepuff of course." The way Madam Pomfrey says it, it seems so obvious. The nurse stands and gestures towards the door, where Professor Dumbledore stood. "Now run along back to your common room, young one. I hear from the headmaster that the troll was apprehended and I'm sure I'll soon have other patients to attend to."

Not wanting to outstay her welcome or undergo the nurse's scrutiny once more, the blonde hops off the edge of the bed towards the exit, not without remembering to nod her thanks. She only pauses briefly by the door, her eyes catching upon a picture pinned to the board nearby. A young Idun, her dark hair in a braid similar to hers, smiles from the picture with a proud looking younger Madam Pomfrey behind her. The black and yellow of Idun's tie is proudly on display.

Elsa doesn't notice Dumbledore's pained look as he winces and leaves. By the time she turns her attention back to the door and exits, he's already disappeared out of sight. She waits until she is clear of the hospital wing before heading to the nearest lavatory and removing her glove. She inspects the thin and pale hand carefully before running the cold tap over it, wincing a little as the bloodied gash on its back stings. Using some of her wandless ice to cover up the wound and cool it down, she sighs. Yet it was with a grin that she puts the glove back on.

Hufflepuff, huh? And with herself and papa in Slytherin and Ravenclaw, all it would take would be for Anna to actually be in Gryffindor, and the family would have all four houses covered. Her smile grows wider. She thanks father for the game. It's definitely helped make Hogwarts feel if not like home, definitely like a family.

Fin