Winter at Hogwarts never arrived quietly.
It seeped into the stones.
It howled down corridors.
It made the castle feel half-asleep, wrapped in frost and crackling fireplaces.
And yet—
The first morning after Christmas break, when students dragged themselves back into routine with the energy of half-dead puffskeins—
Defense Against the Dark Arts was packed.
Because Professor Lupin had promised something "a bit more advanced." After the cocky third years practically demanded something challenging after being egged on by Sirius to almost entirely rebel against the course syllabus
Hermione sat forward eagerly.
Daphne looked sharp and focused.
Cassius sat in the middle of them calm, composed… and mildly suspicious.
Lupin wasn't prone to dramatics.
But today he strode into class with a look that screamed Secret Knowledge Incoming.
His shabby robes trailed behind him, chalk in one hand, a small wooden music box in the other.
"Good morning, everyone," he greeted warmly.
Murmured replies echoed.
Lupin grinned.
"Today we're going to attempt something quite special. Something far beyond the usual third-year curriculum."
There were gasps.
"Yes," Lupin continued, smile widening, "yes, even beyond the freezing spell we've been practicing."
He tapped the board.
White chalk spelled two words in looping, elegant strokes.
THE PATRONUS CHARM
The room went silent.
Hermione inhaled sharply.
Lupin clasped his hands.
"The Patronus Charm is one of the most powerful defensive spells known to wizardkind. A protection woven of positive emotion—pure, incorruptible—capable of warding off the darkest creatures."
Cassius watched the class collectively lean forward.
"It is also," Lupin added gently, "very, very difficult. pull it off and you can pass your O.W.L with ease in your fifth year."
Students deflated instantly.
"However," he continued, eyes twinkling, "I believe learning the foundations will help you all grow. And since you insisted—"
He shot a pointed look particularly at Draco and Harry.
"—I agreed."
Lupin's smile crinkled the corners of his eyes.
"First, before even bothering with the incantation you need to think of a very happy memory, a powerful memory and let it fill you up inside. Then with your wand out chant the spell: Expecto Patronum."
His gaze shifted briefly… meaningfully… toward Cassius.
Already known among the teaching staff a child prodigy, but for Cassius he would expect this particular spell to be impossible to cast first time, simply because he had never bothered trying to cast it before leaving it's level at a measly 0 for right now.
But after a quick muttering of the spell with his wand in hand resulting in a fail, Cassius quickly got to work shifting his army of idles to practicing the spell in his place as he started thinking more about the spell itself.
Expecto was fairly easy to guess: Expecting or near enough.
Then Patronus... Patrone... Patron... Aka a Protector or Guardian.
And then when combined with the known method of using a happy memory, it becomes a guardian called forth to protect a happy memory.
The surprising part about this is that the memory doesnt even need to be real, as evidenced from the harry from the media, his chosen 'memory' to cast his Patronus charm was afterall just a fantasy not something he actually experienced for himself.
So as long as it was something that brought you joy, and was a memory or thing you wanted to protect it would be good enough to call forth your spirit guardian via this spell.
Around the class many had already begun trying to cast the spell, resulting in... absolutely nothing.
Even the ever diligent Hermione and Daphne had knitted brows suffering a setback for once.
Seeing their frustration he turned his attentions to them.
"What were you thinking about when you tried casting?" Cassius asked the pair.
"About all the books in the library."
"About hanging out with my sister."
Their answers were pretty much what he expected to hear to be honest.
"Sorry to say, but that not good enough, not nearly good enough, you need to pick something that makes you so happy it feels like you could explode.
Something that makes you so happy you would protect it with your very life.
Using his stated words as a starting point the two girls lowered their wands and turned their gazes inwards examining their hearts trying to find something that matched his description.
And they both seemed to reach the same answer at the same time as they quickly bowed their heads but it was plain for him to see their ears were burning red.
Cmon seriously he complained in his mind, pretty soon im gonna need to create an alchemical bonk stick to purge the sinful thoughts regularly appearing in these girls heads.
Is it because of me?
I'm the only real difference in the timeline aside from all of them being friends with one another... am i really that bad of an influence?
However seeing that the three were not exactly practicing but were instead just sitting there.
Lupin stopped beside him.
"Cassius," he said softly. "Would you like to try?"
All eyes turned to him.
The child genius how could he not suceed?
Cassius raised his wand.
He breathed once.
He would fail. Intentionally. A harmless misfire.
"Expecto Pa—"
Cassius cut the spell off mid-cast, letting it evaporate in a harmless wisp before the power could form fully.
Gasps echoed.
Even that tiny fragment crackled with intensity.
Lupin blinked—stunned, impressed, and faintly alarmed.
"Very good control," Lupin said carefully. "Just a little bit more effort and you'll reach the spells first stage."
Cassius nodded once and stepped back.
He had revealed nothing.
Thank Merlin.
But several students were staring at him with wide eyes nonetheless.
Harry, across the room, scowled in frustrated jealousy.
The lesson continued.
Dozens of failed attempts.
Tiny successes—Hermione almost produced a wisp with form.
Daphne improved with Cassius's adjustments.
Slowly but surely, the class improved.
And finally—
Lupin clapped his hands.
"That's enough for today. You all did beautifully. Even attempting this is an achievement."
Students sagged in relief.
Books closed.
Bags packed.
Conversations bubbled.
Before dismissing them, Lupin added gently:
"And remember—your Patronus will come when your heart is ready. Not before."
Cassius felt that line linger.
The class filed out, chattering about memories, glowing wand tips, and who might someday produce a full-bodied Patronus.
Cassius walked among them in thoughtful silence.
Hermione nudged him. "You were amazing, you know."
Daphne nodded. "You basically taught us half the lesson."
But as they left Cassius could only have his thoughts wonder once more, when he did cast his patronus what would his patronus actually be?
Afterall following the progression of his life so far, he would probably think a dragon, but the odds of having a magical creature as your Patronus was beyond rare, afterall aside from two known figures to have Phoenix's as their Patronus Cassius could not think of any others who bore one.