Given the success of my Harry Potter/Hellsing crossover, I thought I'd do another one. At least one reviewer wanted a Harry/Schrödinger pairing. Hence this. I may not write slash, but genderflipped characters are a different matter. As with Haemophilia, this had its origins in one of sakurademonalchemist's works. I was inspired by A Deal Made in Good Faith, primarily a crossover between Harry Potter and Supernatural, but it has elements from Ghost Rider and Hellsing, with Schrödinger becoming an ally of the female Harry in that story. Here, he becomes her love interest, and they share origins.

This story had a troubled genesis, going through a few different versions. This one is the one I'm most satisfied with so far, but I'm still not sure whether it has legs, so I'm posting the first three chapters of the current version of The Uncertainty Principle for your perusal.


THE UNCERTAINTY PRINCIPLE

CHAPTER 1:

CAIT SÌTH

There are many variations of the same story, of the child of the Potters. Who is a villain, and who is a hero, varies between each telling of the story. But there is almost always a cottage at Godric's Hollow. There is almost always a prophecy, engineered or not. There are two old men, one who fell into darkness in pursuit of power and immortality, the other who dances so close to the edge, sometimes, he falls into the darkness too, and other times, he stays in the light.

This is not one of the stories where he stays in the light. This is one of those stories where he uses the light to blind people to the darkness within. A darkness that drives him to be a Dark Lord from within the light.

And there is a child. In this story, it's a girl. Even if she isn't human. A girl on whom the fate of an entire society rests. One who will become famous through tragedy.

Where it begins is tricky. It could begin in Wallachia, centuries ago, where a man with a dark past becomes a monster. It could begin when an English lawyer makes a fateful journey to Transylvania. It could begin with an argument between two brothers, a sister, and a charismatic young man. It could begin when an inbred witch, desperate to escape her impoverished life, ensnares a local landowner with a love potion, and out of a loveless union, a child is born. It could begin during the Second World War, where, while two wizards clash against each other, an ancient vampire and a teenaged assassin attack a Nazi facility in Warsaw, Poland. It could begin where a couple, desperate for a child of their own, willingly adopt a baby girl who isn't even human, while half a world away, a boy of the same species is born into the custody of a surviving group of fanatics. It could begin when a girl is left on a cold doorstep by a meddling old man with, in this story at least, less than benign motives. It could begin when a young girl, desperate to save herself from a treacherous uncle, manages to revive an ancient monster, who swears itself to her service.

Where to begin the story? That is, indeed, the question. Perhaps we should start at the time when a girl met a boy. Like many such meetings, it happened quite by accident and coincidence, and yet, catalysed something greater. It begins with the girl fleeing her home, and her relatives, not knowing that bonds on her all her life, bonds which had been rotting since she was nearly killed by a Basilisk, were about to snap…


Rose Potter knew she was in trouble. She was stranded, lugging a huge trunk through the darkened Magnolia Crescent, and may be on the verge of being expelled from Hogwarts after turning that vile woman she was forced to call Aunt Marge into a human zeppelin. And something had felt different for a while. It had done ever since the Basilisk bit her as she killed it, ever since Fawkes watched on, seemingly letting her die, despite her desperation not to…

…Only for her to survive. One moment she was dead, and the next, she was alive, albeit with black smoke pouring out of her scar, screaming, and the shade of Tom Riddle staring at her incredulously. And shortly after killing the spirit within the diary, the Sorting Hat had remarked rather enigmatically that she was being set free, and told her to tell everyone that Fawkes had used Phoenix tears on her wounds.

She didn't understand what she had begun to feel during the weeks she had spent at Privet Drive. At first, she thought it was part of puberty hitting her. After all, she had recently gone through her menarche (and Aunt Petunia, for once, had been merciful enough to buy hygiene products for her). But she got the feeling this was something else.

It felt like something within her was straining to get free. Like parts of her that were missing for the longest time. One thing she had was very good (even supernatural) night vision, and an extremely good sense of smell. Sometimes, Hermione would claim that Rose's irises seemed to glow gently in the dark of the dorm, like luminescent emeralds. Hermione would tell Rose that she reminded her of a cat at times, alternating between playful and unsociable. Rose was struck by the comparison, especially as Luna Lovegood, a Ravenclaw who had come to Hogwarts last year and was a friend of Ginny's, made enigmatic comments about Rose and cats.

Rose was definitely a cat person. If Hagrid hadn't gotten her Hedwig, then she would have gotten a cat at Diagon Alley. She even got along with Mrs Norris, Filch's cat, and she had, if not a friendship, then a more cordial relationship with the Squib than almost any other student in the school thanks to that. It was almost as if she understood what Mrs Norris was saying.

As she came to a stop, exhausted, she contemplated her options, given that she was up a certain creek without a paddle. It was while she was considering becoming an outcast, using her money to fund a life in exile, that she sensed something nearby. She could smell something…something between dog and man. And she didn't know why that came to mind. She turned carefully, her eyes roving the dark, until she froze upon looking between the alley and garage. She could see faintly what looked like a massive black dog. And its eyes, shining in the darkness, were looking at her.

She was frozen in place as it trotted up to her. Even in the darkness, she could see that, although large, there was something vaguely pitiable about it. It looked emaciated, with matted fur. But she was still wary. Her instincts were screaming at her.

Suddenly, the dog shifted, and changed. Where a mangy dog once stood, an emaciated, ragged man, with matted black hair and a beard. His grey eyes danced feverishly. With a thrill of horror, Rose recognised him as the escaped murderer she had seen briefly on television, Black if she recalled his name.

For a moment, they stood staring at each other, Rose frightened out of her wits at having an escaped murderer facing her down. And if he had changed from a dog, what were the odds that he was a wizard?

Then, the man asked, in a hoarse voice, "…Rose?"

Shit, he knew who she was. Then again, given the scar…

"Stay away from me," she hissed in fear. She wanted to be anywhere but here. She only distantly noticed that the look on his face was not of someone trying to attack her, but of concern. The rest of her wanted to get away.

Suddenly, something broke within her. Suddenly, a power flooded right through her, and it felt natural, like it belonged, even as it seemed to overwhelm her. It was as if she was spread out across the world, no, the universe, and she could be anywhere she wanted to be.

And so, she leapt.


Sirius Black stared at the empty space where his goddaughter used to be. For a moment, he was merely astonished. Then, he realised something. Just before she vanished (and without the distinctive crack of Apparition), he thought he glimpsed a pair of cat ears appearing from beneath her messy mop of black hair.

It took a moment for him to process it, before a long-buried memory rose from its grave. A painful, rueful smile touched his lips. He only hoped that his goddaughter would be safe, wherever she ended up…


When she was young, Rose, in order to escape Dudley and his merry little band of bullies, had teleported up to the roof of the school. She had been slapped around by her uncle and thrown into the cupboard for that. When she discussed the incident with Hermione and Ron during their first year, Ron had called it Apparition, with Hermione speculating that it was perhaps accidental magic. But some part of Rose knew that they were wrong.

She found herself in a library of what looked like an old mansion. Rose knew that Hermione would be drooling at the arrays of books on dark wooden shelves. She certainly was. She wasn't quite as overt about being a bookworm as Hermione was (and to be fair, Rose preferred reading fiction to textbooks, whereas Hermione was equally at home with both), but she was definitely a bibliophile, and for a moment, she facetiously wondered whether she had died and gone to heaven.

"Rose?"

The voice came from behind her, and she whirled to face it, idly wondering why her ears felt different. There was a painting on the nearby wall, and she recognised two of the people on it. One was a young man with a shaggy mess of black hair and hazel eyes. The other was a young woman with red hair and emerald eyes. Her parents. She recognised them from the photo album that Hagrid had given her at the end of her first year.

But the third person was another matter entirely.

Rose realised, with a shock, that she resembled this third person, a seemingly-young and very beautiful woman, more than she resembled her parents. The woman seemed to be in her twenties, with a messy shock of black hair, green eyes that almost glowed, and dressed rather casually. Her parents were dressed, while not formally, a bit more conservatively, whereas the woman was dressed in jeans and a shirt. The shirt had Hello Kitty on it(1). Which, in a way, was rather appropriate.

After all, the woman seemed to have a pair of cat ears poking through her hair. And was that a tail protruding from a hole in the woman's jeans?

"Mum? Dad?" Rose asked in a quiet voice.

The three people smiled at her warmly, though the cat-eared woman then looked at the other two. "I think we'd better ease her in. We need to find out what happened, first. She should have been here ages ago," the woman said with a musical voice that had an Irish lilt to it.

Lily nodded, before looking at Rose. "Rose, darling…who's been raising you? Please tell me it's Padfoot…I mean, Sirius."

"Sirius? No, it was your sister and her family," Rose said bitterly.

James Potter facepalmed. "Ugh, you called it, Lily. That old goat wouldn't leave it alone. I'll bet he's sealed our wills, too. He knew we didn't want Rose to go to that horse-faced hag! That's what Padfoot was for!"

"Who is that?" Rose asked. Was she meant to go with someone else all this time?

"Sirius Black," Lily explained.

Rose's eyes widened. "That escaped convict…the one on the TV…I was meant to go with him?!"

"Convict…oh, shit," the cat-eared woman said, facepalming herself. "Looks like your diversionary tactic backfired. Pettigrew must've framed him. Bastard."

"Catriona(2), language," Lily said. "I told you not to swear in front of Rose, remember?"

"Look, can someone please tell me what's going on?" Rose demanded.

The three of them looked at each other, before they nodded. And so, they began to tell her what she needed to know…

"Okay, so let me get this straight: because of some prophecy uttered by the current Divination teacher of Hogwarts, Voldemort targeted me. We went into hiding using something called the Fidelius Charm, where only the Secret Keeper could tell people where we were hiding. Sirius Black claimed to be the Secret Keeper as a decoy, but it was actually Peter Pettigrew, who must have betrayed you, and he somehow framed Sirius. I'm currently in the Potter Manor. Have I got that right?" Rose asked.

"Yes," James said. "I thought something was up when nobody came here. Well, apart from one person, that squatter who sometimes comes here. But Rose…there's more to this." He pointed over at a mirror Rose hadn't noticed. "Have a look in the mirror."

Rose did so, and recoiled upon looking into it. She looked different now. After all, she was certain she hadn't had cat ears before, poking out through her hair. She reached up, and gently tugged on them. Yep, very real.

Catriona now spoke. "This might be hard for you to grasp, Rose…but James and Lily are not your parents, at least not by blood, anyway. You're not human, Rose. Not wholly, anyway, thanks to the adoption potion James and Lily gave you. I am your mother. Like me, you are a Cat Sìth."

CHAPTER 1 ANNOTATIONS:

So, Rose is at the Potter Manor, and she has just learned that she isn't human. Now, what does this have to do with Hellsing, I hear you guys ask? Read on and find out. Schrödinger will make an appearance before long, and so too will Alucard and Integra, though not until later for those two.

In Haemophilia, Schrödinger was more of an experimental hybrid between human, cat, and House Elf. Here, he (along with Rose) are Cat Sìth. I'm taking some liberties with the original legends of the Cat Sìth, but it helps. Not all Cat Sìth have powers like Schrödinger (or Rose, as we'll find out). And keep in mind that Fawkes let Rose 'die' in order for her powers to be re-awakened. Fawkes is most definitely on Rose's side. The Basilisk venom merely triggered her ability (like Schrödinger) to undo her own death. We'll explain that later.

1. Hello Kitty made its debut in the Seventies, so it's not out of the question for Catriona to be wearing a T-shirt.

2. Catriona is pronounced 'Katrina'. Gotta love the Irish language. It means 'pure', though I chose it for the bad cat pun. Hey, it was either that or Leona, and I wanted an Irish name.