A/N: The title is Latin for 'Sun and Moon', provided by my best friend, and one of the best writers on the site. Also, in light of my difficulty beginning, the first chapter will contain a significant amount of verbatim text from Prisoner of Azkaban, though less so at the divergence.
Chapter 1: Lycan Rebirth
The grounds were very dark now; the only light came from the distant windows of the castle. Without a word, they set off. Pettigrew was still wheezing and occasionally whimpering. Harry's mind was buzzing. He was going to leave the Dursleys. He was going to live with Sirius Black, his parents' best friend...He felt dazed...What would happen when he told the Dursleys he was going to live with the convict they'd seen on television...!
"One wrong move, Peter," said Lupin threateningly ahead. His wand was still pointed sideways at Pettigrew's chest.
Silently they tramped through the grounds, the castle lights glowing slowly larger. Snape was still drifting weirdly ahead of Black, his chin bumping on his chest. And then -
A cloud shifted. There were suddenly dim shadows on the ground. Their party was bathed in moonlight.
Snape collided with Lupin, Pettigrew, , who had stopped abruptly. Black froze. He flung out one arm to make Harry and Hermione stop.
Harry could see Lupin's silhouette. He had gone rigid. Then his limbs began to shake.
"Oh, my -" Hermione gasped. "He didn't take his potion tonight! He's not safe!"
"Run," Black whispered. "Run. Now."
But Harry couldn't run. Ron was chained to Pettigrew and Lupin. He leapt forward, and Black tried to catch him, but missed.
As Lupin transformed, Pettigrew grabbed the fallen wand, and before Harry could stop him, he began to transform. Lupin finished transforming and turned to face the two boys, and lunged. With Ron unconscious, having fallen hard and hit his head on a rock in the scuffle with Pettigrew, hindered by his damaged leg, Harry did the only thing he could think of. He threw himself between the attacking werewolf and his unconscious friend. His howl of pain was nearly as terrifying to Hermione as Lupin himself, the incredible pain blinding him as the sharp claws left deep, bloody wounds across his back.
Harry had fallen on all fours from the force of the blow, but he struggled to rise to his knees, and his entire body twitched and spasmed from the entirely new level of pain that followed, and he fell again to his knees just a few feet away from his friends. Lupin sniffed the air, but otherwise remained inexplicably frozen.
Hermione and Sirius could only watch in horror, both extremely aware that Harry was now irrevocably tainted, marked as a werewolf and with all the stigma Lupin was familiar with, though none of that crossed their minds at the moment. They were more concerned with the fact that usually, even during a full moon, the infected didn't transform right away - and even when they did, it rarely resulted in the obvious level of pain the Boy Who Lived was currently displaying.
For Harry's part, very little was filling his head besides the pain. His world had turned white ad every fibre of his body felt as if it were being set on fire. He was only dimly aware of his body becoming heavier, longer, broader. He experienced every inch of his new muzzle ad the bones shifted, and he felt his nails and teeth lengthening, sharpening. By the time the pain had ceased, he was aware of every new feature he boasted, from the muzzle fangs and claws, to the coarse hair, the sharper senses, and the bestial strength that courses through each of the solid muscles layering his formerly skinny, now large frame.
By the time Harry stood, the tattered school robes loose around him, Ron had woken, and stared in horror at he beast who stared briefly with familiar green eyes. Hermione had backed up and Sirius had moved to shield her from his godson and the now seemingly docile Lupin, who crouched on all fours, a vague expression of fear and respect on his lupine face, his lanky form - once terrifying because of its hidden strength - looking pitiful compared to the solidly built counterpart who stood before him.
They all watched as he stood, locking eyes with each of them briefly before turning his furred, clawed hands over before his eyes, noticing the jet black color of his fur, and finally threw his head back, and howled. Hermione shivered, staring wide-eyed at her best friend, falling to her knees with tears on her cheeks as the sheer animal power of the howl tore through her, a challenge and welcome in his voice. When he finished, he turned his gaze back to Ron, then Lupin, then Hermione, and finally to Sirius. He raised his hands to his head and howled, this time in pain, as a faint aura of magical energy surrounded him. When it dissipated a few moments later, his hands fell limp against his sides, and his eyes, filled moments ago with nothing but animalistic fury, were now almost quizzical, and he took a step towards his friend and godfather, an arm raised, though it fell, stopping him in his tracks, when he noticed Hermione flinch, turning away with her arms raised ad if to ward off an attack. Sirius simply stared, paralyzed with fear and a strange urge to roll over, but noticied the new look in Harry's eyes.
As he stared, Harry closed his eyes, amd within seconds began to shrink slightly - but not nearly as much as he should have. Before Sirius' eyes, his godson emerged from the lupine creature, though different. His body was now nearly as tall as Sirius himself, and - much to his surprise - somewhat broader in the shoulder, the muscles lining his body, visible through the shredded robes, were neither extraordinary nor insignificant; they simply gave the impression of a powerful young man, rather than a scrawny child. He looked otherwise unchanged, barring the faint growth of facial hair which even now continued to recede, though it did leave behind the faintest hint of a shadow, lending him the appearance of a man several years older.
"S...Sirius? Hermione? Harry croaked, his throat rough still from the rapid series of transformations. He nearly stumbled as he stepped closer, but caught himself, firmly gripping Sirius forearm when he offered it to Harry to catch him. He paused, and spoke again after a few brief moments. "What...what happened? I feel...different...stronger..." Sirius looked as confused as Harry felt, and Hermione, though no longer as fearful ad she had been, still looked nervous, tinged with a trace of remaining fear, betrayed by the subtle twitch of her hands, despite being folded inside her robes.
A whimpering sound caught their attention and they saw Lupin, huddling with his hands on his head, fangs bared into the forest, roughly the same direction Pettigrew had been seen heading. This was the only reason they noticed the hooded figures, dozens of them, emerging from between the trees, though the horrific chill made it all to clear who they were. Sirius seemed paralyzed, his face once again pale as a sheet, and both Ron and Hermione had already fainted from the oppressive cold of the large swarm of Dementors. Harry reached for his wand, fumbling in his robes for a moment, before pointing it at the approaching figures.
"Expecto...Expecto Patronum!" Harry roared, putting all of his dreams of a new life with his godfather into that single spell, sure that it would be enough. As he watched, a faint cloud of silver, vaguely forming into a four-legged shape, quickly dissipated, causing Harry to growl. He repeated it again amd again, failing each time, before he realized he felt somewhat more tired then before, which was a new experience. With a scowl he stuffed his wand into his robes, and began to think. As he remembered how Sirius had claimed to escape Azkaban, he decided to listen to the instincts clawing at his conscious mind, baring his teeth much like Lupin had as he transformed yet again. As he muscle and fur covered his body once again, he growled, meeting Lupin's eyes, and crouched, facing the closing swarm of creatures before breaking into a run. He could feel the wind rushing past his face, through his fur, and was reminded of flying for a few brief seconds before he was close enough. With a howl that would have chilled a human to the bone, he leapt into the air, tackling the lead Dementor and dragging it to the ground.
As he straddled the dark creature, the next few minutes would be difficult for Harry to recall in the immediate future, which he became grateful for as the memories returned.
He lifted one heavy hand in the air, and brought it down in a sweeping motion, dragging his claws through the Dementor's face, thick grey blood clinging to his claws. For several seconds more he rapidly swiped at the corpse, barley stopped by the piercing, unearthly scream that filled the brief gap between his first and second blows.
After a decided the creature was no longer a threat, he stood and noticed the creatures had given him a wide berth, but had still continued forward, nearly upon his friends. Breaking into another run, he bowled over several Dementors in passing, making sure to dig his claws in, if only for a second, as he shoved each out of his way. He was vaguely surprised to see Lupin still there, standing on two legs as he swiped frantically at the vile things that surrounded him. Seeing one Dementor approaching the older werewolf from behind, ghastly arms outstretched, he leapt and used a nearby Dementor as a stepping stone, launching himself into the air again to land feet first on his target, giving its head a swift kick before leaping away again, grunting in satisfaction as it screamed, and he dispatched several more that happened to be within arms reach.
His next target was the Dementor currently attempting to Kiss his godfather, gripping its yielding neck in a powerful grip before pulling it backwards, venting his rage in a brutal execution by forcing three of his fingers into the shapeless maw and gripping it as he pulled, leaving the Dementor to stumble through the air with its face flapping freely, rendering the creature even more disgusting, as he would later realize. The brutality of the move penetrated even the mindless hunger of the monsters, and they slowly began to drift away, still watching him closely, though they didn't leave.
Harry decided to fix that.
Flying into the air with yet another running leap, he grabbed the shroud of a fleeing Dementor, reeling it in like a fish as it screamed. Its screams were justified when he finally managed to place both of his hands on its skull, pressing until he held nothing but bone, grey blood, and a pile of gore he presumed to be its brain. This final assault proved enough to curb their endless appetites, and they quickly fled, returning to wherever they had come from.
As he watched the last of them disappear over the treeline, he slowly shrank, returning to his human form, and turned. He noticed Lupin, still transformed, staring at him curiously, while his friends began to wake. With a faint smile on his face, he took a step towards them - and collapsed.