Disclaimer: Harry Potter is owned by J. K. Rowling, and the rest is mine, although inspired by the works of Games Workshop (Tyranids), Blizzard (Zerg), Jim Butcher (Vord), and probably a bunch of people I forget.

Intro: Story begins the morning of November 23, the day after Harry is shown the dragons by Hagrid. Inspired by Harry Potter and the Swarm by Beyogi, but I'm basing my swarm more on Tyranids than Zerg. Heavily modified though, to the point where I don't think this even counts as a crossover. Case in point: There is NO Warp in the Potterverse. I will assume zero knowledge of tyranids, and although I'll be using some base creatures (ripper swarms, genestealers, 'gaunts, etc) they will be modified, so don't assume they are the same.

Chapter 1

Spawning the Swarm

"No Harry! I'm sorry, I just can't take it any more." Hermione said, before turning and rushing away, leaving Harry in shock. What was that about? Harry wondered briefly, before being brought back to himself by the mocking laughter of a nearby gaggle of girls. Flushing, Harry jolted forward and rushed out the portrait hole, determined to catch up with Hermione and find out what had happened to make his only friend abandon him.

Emerging into the corridor, Harry looked around and couldn't see any trace of her. His shoulders slumped with defeat, Harry turned and began to trudge away.

"Hey, Harry?" a voice called behind him. Harry turned, and saw that Neville had come out behind him. "You're not going to breakfast?"

"No, don't feel like it Neville." Harry replied. The smaller boy smiled vaguely at him, then left in the direction of the great hall. Harry resumed his wandering.

Great. Everyone abandons me. All alone..." Deep in thought, Harry found his way to an uninhabited section of the castle, where he paced back and forth, brooding. God, I wish I had someone, anyone, I could trust! I wish I had someone who would never abandon me... Someone I could always count on... Someone who would put my needs first for a change... Although really, I'd settle for some thing at this point! Harry thought with a chuckle.

"Merlin! Where did that come from?" Harry exclaimed, seeing a door appear suddenly in the wall in front of which he had been pacing. Bored with brooding, Harry shrugs and opens the door.

Behind the door is a small room, with plain, unadorned grey stone walls, entirely empty except for an ornate diagram painted on the floor, at the centre of which sat a book.

Harry picked up the book. A slim volume, bound in brown leather, the title of the book was embossed in raised gold lettering on the front. "The Familiar Way, or, the Path of Forking Gardens". Harry read, curiosity driving him to open it. The letters within seemed to swim and writhe before him, making his eyes water, before settling into recognizable shapes.

Harry read the first page, then, with mounting excitement, the first chapter, and then before he knew it an hour had passed and he was still standing in the bare, cold room, feet aching, cradling in his hands what he knew was the answer to all of his problems.

Forgetting the dragon that awaited him in the forest, forgetting the shade of Voldemort that plotted against him even now, forgetting even the Herbology class he was supposed to be attending, Harry read. Once, twice, again, until the words were burned into his memory, and he felt as if the incantation was pressing at his lips.

Gently placing the book on the ground beside him, Harry stepped to the edge of the carefully drawn diagram on the floor. Raising his wand, he began to chant, calling aloud the words of magic, the alien speech of an ancient tongue bursting forth from his mouth like a cresting wave.

Around him, the magic built; shimmers of energy filling the air with colours, radiant spikes lashing out, as the space before him twisted and warped. He could feel his magic reaching out, out, far beyond the reach of any mortal mind, questing for something...

And then there was stillness. An expectant silence, as magic danced in the air, and his shadow stretched out for miles behind him. Harry raised his wand once more, and called out the words of summoning.

"I call the one that would be bound

Across the void of time and space

That which was lost shall now be found

Come forth into your proper place!"

With a roar like the sound of a distant ocean, all the power that had built up in the room rushed forth. Shifting, twisting, warping space and time to reach into a distance place, and otherness. Where what was, was not, where up was left and down was through, the magic of the ritual brought into existence a being that never was, and never otherwise would have been.

Gasping for breath, sweat standing stark and chill upon his skin, Harry knelt, and stared. In front of him, was a creature the likes of which he had never seen before. Vaguely snake-like, it had a long, writhing tail, a series of tiny claw-like feet, and was entirely covered in a dark, chitinous armour. Its eyeless head terminated in an oversized mouth, filled with jagged, serrated teeth – he could see it was undoubtedly capable of inflicting some serious harm, even if it was less than three feet long.

Stranger still, Harry could feel it, as if it was a part of his own body. He willed it to move, and it moved; squirming across the room much more swiftly than he had expected it would be capable of. Without any mind or will of its own, it was merely an extension of his body; he could move it as easily as his own limbs, and could feel what it touched as if it was his own skin.

Beyond that, he could feel it's hunger, a gnawing craving to devour, and at the edge of his mind there was a sense of terrible potential – as if this little creature could become something enormous, something extraordinary.

Harry smiled, as he began to understand what it was that he had summoned. Then he laughed; This was perfect! He would never be alone again – this little pet would never, could never leave him, for it was a part of him.

Then the door swung open. Hermione stepped through. "Harry!" she gasped, horrified at seeing her friend gasping on the floor, apparently incapacitated with a horrifying alien chittering behind him.

"Impedimenta! Stupefy! Impedimenta!" Hermione called, casting as quickly as she could, while rushing forward to protect Harry.

"No, wait, stop!" Harry called, while his new familiar darted back and forth at Harry's command, dodging the spellfire. "It's friendly, don't hurt it!"

Slowly lowering her wand, Hermione kept a wary eye on the creature. "What is it, Harry? This isn't another one of Hagrid's, you know, things, is it?"

"No, this is mine. It's my familiar – I summoned it with this book..." Harry paused, looking frantically around. The book had disappeared. Deciding he had more important things to worry about than a vanishing book, Harry rushed on with his explanation. "I was just thinking about how I wished I had someone who would always stand by me, no matter what, and then this door suddenly appeared, and I went in and found a book on how to call a familiar, and I did it, and I have this!" Harry smiled broadly, gesturing at his new appendage as it scuttled forward to stand next to him.

"Oh, Harry," Hermione sighed, "I'm so sorry! It was just, they were saying such horrible things, and the thought of facing them just got to be too much."

"It's ok" Harry said, "I understand. What changed your mind?"

"Well, when you didn't come to class, I got worried."

"I asked the portraits where you were", she continue, "And they lead me right to you. No one hardly ever thinks of them, but they see everything that goes on in Hogwarts."

"I'm hungry" Harry said abruptly. It was becoming increasingly difficult to separate the needs of himself from his familiar, and the creatures gnawing hunger was growing by the minute. "It's lunchtime, right? Let's go and get food."

"No Harry, lunch isn't for another half hour. We're, well, we're supposed to be in care of magical creatures right now." she said with a guilty grin.

Harry felt bad for a moment, knowing how hard it must have been for Hermione to skip a class, and feeling guilty for causing her discomfort. Then his guilt was washed away in waves of hunger. "Sorry, but I'm really, really hungry", Harry said, making for the door, his familiar at his side.

"Hold on Harry, you can't just walk around Hogwarts with that!" she pointed out, then asked, "And what is it, anyway?"

Harry replied with a frown, "I'm not sure, I don't think it has a name, but it feels like, Reaper. I'll call it that. I didn't bring my cloak though, any of you have an idea what I can do with it? If I don't feed it in the next hour or so, it's going to die."

"I thought you said YOU were hungry?" Hermione questioned.

"It's, well, it's like it's a part of me. I can feel its hunger, and move it around just by thinking it."

"That makes sense" Hermione commented, "I noticed that Fawkes always seems to know what Professor Dumbledore wanted, so probably all familiars are like that."

Seeing that Harry was looking impatiently at the door, Hermione opened her bag, and started removing books. "Here, you can help me carry these, we can put your little pet in my bag."

"Is it really going to fit?" Harry asked, seeing that her bag was barely half the size of the Reaper.

Hermione smiled. "It will fit. I had space-expanding charms cast on my bag, so I could keep all the books I needed with me."

Once the last of her books had been removed, Harry had his familiar scurry into her bag, which Hermione insisted he carry, not wanting to be so close to the creature herself.

oOoOoOo

"Where are we going?" Hermione asked.

Harry had led them a roundabout path, obviously hoping to avoid getting in trouble by being caught skipping class, but it was now clear that they were headed for neither the kitchens, nor Gryffindor tower.

"I was just thinking, I'm so hungry, I could eat a tree" Harry replied, "then I realized, Reaper here actually can eat a tree – so, we're going to the forest. There'll be plenty of food there."

Luckily, they made it to the forest without incident.

The middle of the day was hardly the best time for sneaking out, and neither of them – if they had stopped to think about it – would have expected to make it without interruption. Luck, it seems, was on their side; Or, perhaps, it was simply the dozens of extra students there for the tournaments, that kept the staff occupied and away from the windows.

Whatever the reason, the duo made it safely to the forest, where they were plunged immediately into shadows. This late in the year, the sun lay low in the sky, and the dense canopy of leaves blocked what little light there was.

Hermione pressed close to Harry's side, drawing her wand with a muttered "Lumos". Every little sound, every crack of a twig or rustle of leaves, startled her, and she stared into the darkness as if expecting to be jumped at any moment.

Uncaring for her wariness, or perhaps simply unaware of it, Harry set a brisk pace. Soon, they were deep in the forest, out of sight of the school, and Harry sent his familiar squirming out from the bag, and plunging deep into the wood of a nearby tree.

There was a moment of silence, and then with a tremendous grating, crunching sound, the tree began to collapse in on itself. Slowly inking to the ground, the could see the chitinous flesh of the familiar winding through the wood, its teeth ripping and boring as it shredded trunk and branch and leaf.

Within minutes, nothing remained of the tree but a scattering of chips, and a the Reaper, now nearly four feet tall, and bloated like a balloon.

A shaft of golden sunlight filtered down through the gap the tree left, a single solitary spark of day amidst the stygian gloom of the forest, illuminating the insectoid figure.

Hermione gaped at it, and it turned its eyeless head towards the two of them, as if it could sense their presence.

"Oh Merlin" she said, "What was That?"

"That's the Reaper", Harry replied absently. "It's job is to gather food, and then take it to the digestion pool, where we absorb it so that we can use it." His gaze unfocussed, Harry seemed to be listening to something neither of the others could hear.

In fact, he was concentrating on his familiar, feeling the sense of potential within it unfolding, giving him a greater understanding of what it was doing and why.

Hermione had now stepped away from Harry slightly, and was looking at him strangely. "Harry, how did you know that? And what's this "we" stuff?"

"I don't know how I know," Harry answered, brought back to earth by her voice. "I just, sort of feel it I guess. It's like, the Reaper doesn't have a mind, but it does have a kind of, genetic memory I guess, and being connected to me lets me understand what it is and how it works."

"It's creepy" Hermione commented. "Can we go back now? I'm sure it can't still be hungry, but it's almost lunch, and I am!"

"I can't go." Harry said.

"Well, you have to. We're breaking enough rules as it is, you don't want to get in even more trouble, do you?" Hermione asked, bossy as ever.

"No, I mean I can't go back. I have a, a synaptic connection to the Reaper, and if I go more than a few dozen feet away from it, it will die."

"You can't just stay in the forest!" Hermione retorted crossly.

"You're right", Harry said. He raised his hand, and the Reaper began to twist in on itself. As they watched, it seemed to shrink and dissolved, a sickly green liquid leaking from tears that appeared in its sides. Slowly the creature shrunk down, until all that was left was a pool of softly bubbling green goo, around six feet wide, and edged around with a ring of the same chitinous flesh that the Reaper had been made of.

Surprised by the transformation, which was no less shocking for being slow, Hermione positioned herself directly in front of Harry, crossing her arms and glaring at him, wordlessly demanding an explanation.

Harry sighed, feeling much more himself now that his unnatural hunger had been sated and his Reaper's purpose fulfilled.

"It's still the Reaper, just in a new form now. See, the Reaper's are like larvae. They only live for a few days at most, and just have to survive long enough to gather enough biomatter, then they can transform into something else. This one became a digestion pool, with can absorb any biomatter dumped into it, and use the energy to spawn Reapers, which can then harvest more food, and turn into other, more useful creatures and, well, buildings."

Hermione tilted her head, a dubious expression on her face. "Buildings, huh? Like what?"

"Well," Harry began, "Like a synapse node, which acts as a sort of mental relay. Or a spawning chamber, that can produce larger creatures than the Reaper, that are capable of more things." Suddenly Harry smiled, as his mind filled with ideas and images, a plethora of fanciful creatures dancing through his imagination. "Hermione, it's amazing – these things have so much potential!"

Concentrating on his sense of the digestion pool, Harry mentally queried what it could produce now.

Stored bio-energy: 0 units

Potential spawns: Reaper (1 bio-energy), Guardian (40 bio-energy)

Rushing forward, Harry pocketed his wand and started gathering armfuls of fallen leaves and twigs, and dumping them into the pool. "Come on, help me get more food!"

"Harry, we need to get back to the school. You can't just stay out here. Look, how about we ask Hagrid to watch your, your pool, I'm sure he'd be happy to take care of it."

Not stopping his work gathering fallen branches, Harry answered her seriously, thinking fast. "No Hermione, we can't tell Hagrid. Or anyone, for that matter. They wouldn't understand – these things are just too different. Can you imagine what they would do if they found out? I mean, just look at how they treat house elves! You wouldn't want to subject a whole new species to that kind of enslavement, would you?"

Hermione glared at him again. "fine, but you are coming back with me, or I WILL tell someone."

"I can't leave the pool unattended, anything could happen to it. Once I get more than a dozen feet away, I won't be able to control it, and it will just sit there until I get back. I know I need to be back tomorrow for the first task, so I'll tell you what. You help me gather enough biomatter to spawn a guardian to protect the pool, and as soon as that's done, and then I'll go back with you."

"And you'll stay in the school then, right? Harry?"

Dropping his last load of wood in the pool (Current bio-energy: 0.03 units), Harry walked up to Hermione. Placing his hands on her shoulders, he looked her deeply in the eye, and spoke in the heaviest tone he could manage.

"I need to come back out here. Don't you understand? This is my chance – my opportunity to be part of something bigger. I've always wanted to be part of a family, and this is my chance. Whether it was luck or destiny that brought me the Reaper, it has given me the opportunity to do something truly incredible, and I can't let it just slip away."

His eyes locked on hers, Hermione felt herself flush under the intensity of his gaze, feeling uncomfortably aware of his closeness.

"This isn't just about me, Hermione. This is also about Voldemort. No one could beat him last time, and we both know he'll be back eventually. What's going to happen then? Don't you see? It's inevitable – I have to do this. It's my only chance, the only chance for the whole wizarding world!"

Unable to look away from the sudden intensity of his bright green eyes, Hermione felt her certainly falter in the face of the passion in his words. "Ok Harry, if, if it's really that important," Hermione answered faintly.

Together, the two of them worked hard to bring down one of the larger trees, with a combination of cutting and blasting charms. They then levitated it into the digestion pool, and Harry felt the accumulated bio-energy grow to 1.32.

"Ok then" He said, "that should do it."

"That's enough to spawn this guardian thing?" Hermione asked, expecting him to say yes. It had been a rather big tree, after all.

"No," Harry smiled at her with gentle humour, causing her to blush unaccountably. "But it's enough to spawn a new Reaper, which will bring in another tree, which will speed up the harvesting. I have to stay to supervise, though – but you should go."

A quick tempus spell let Hermione know that it was nearing the end of lunch, and that she had better rush to make it back in time for her Arithmancy class.

So with a nod and a quick "see you later", Hermione set out at a run for the school, hoping to avoid losing any points for lateness.

"Right then" Harry said to himself, "Time to get to work."

With a thought, he triggered the pool to begin spawning an Reaper. It took nearly a half hour to do so. The newly spawned Reaper rushed out, and set into a nearby tree, consuming it within a matter of minutes. Returning to the pool, the Reaper dived back in, dissolving into the sickly green goop. It took almost ten minutes to finish digesting the Reaper, at which point the collected bio-energy had risen to roughly 2.5 units, and Harry immediately ordered the spawning of another two Reapers.

At this rate, it would take several hours to gather enough bio-energy to product a Guardian, and Harry inevitable found his mind drifting back to what had been a constant worry of his for the last three weeks. Namely, how he was going to make it through the triwizard tournament.

Although he had often wished for some clue as to what he would be facing, somehow knowing that the first task would be dragons did not actually bring him any comfort.

By 6 PM that evening, Harry had managed to gather 60 units of bio-energy. By sending his Reapers out to the furthest range of his link with them, he had worked hard to prevent the forest from being completely stripped bare, but still the tree coverage nearby had decreased markedly. A worry for another time, he thought, as he triggered the spawning of a Guardian and another Reaper.

The Guardian was large, heavily built creatures, roughly eleven feet tall and built something like a centaur, with a four enormous legs and a raised body with two arms. Unlike a centaur, however, these creatures were wrapped in layers of steel-hard chitin, their heavy limbs strong enough to arm wrestle a giant, or to punch through a thick steel plate with their razor sharp talons.

Guardians have no intelligence of their own, although they are capable of following simple orders. Left to themselves, their instinct is to stand firmly in one place, and destroy any creature that comes too close. They need to stay near to a digestion pool as well, as they require two units of bio-energy every day to maintain themselves. The pool spreads a number of tendrils for some distance around itself, with the Guardian (and any other creatures in the swarm) connect to to draw sustenance from. This allows the creature to be solid muscle and armour, without the need for the large digestion tract that provides a weak point in ordinary creatures.

It took two hours to spawn the guardian. Harry mentally ordered it to guard the pool and not kill any humans, then started his own slow way back to school, taking the Reaper he had spawned to protect himself, in case he ran into trouble on the way – the forbidden forest was hardly safe to wander about in alone, particularly after dark, and unfortunately the one Reaper was all that would fit in the bag which Hermione had left him.

Tomorrow, he would face a Dragon.