Next morning, after breakfast, Cassian stood in front of the third-year Gryffindors and Slytherins, adjusting the chalk on the edge of his desk with one thumb. A few students were still shuffling into their seats, robes half-buttoned, hair damp from a rushed wash, and at least two were trying to whisper an entire summer recap under their breath.

He gave it about three seconds before snapping the chalk in half to establish dominance. The room went quiet.

“Brilliant. Now that you all remember you’ve got ears, let’s get on with it.”

He was about to launch into the day’s topic when Malfoy piped up.

“Sir,” he said, all wide-eyed innocence, checking if Potter heard him. “Can we learn about Dementors? I’m curious where they come from.”

Cassian gave him a long look. Not annoyed, more like he was weighing whether it was worth the breath.

“Sure. Let’s all take a merry little stroll through the history of despair.”

A few quills scratched hurriedly into place. Cassian flicked his wand toward the board. White chalk jumped up and scrawled ‘Dementors: Origins, Theory, and Why They’re Terrible Company at Parties.’

“Long version or short?”

Dean raised a tentative hand. “Short?”

Cassian squinted at the back row. “Cowards. You know there’s no short in History.”

A collective groan rippled through the class.

He snickered. “Dementors is a love story.”

That earned him a full gasp from at least six students. Malfoy made a noise. Pansy let out a strangled giggle.

Cassian just grinned and flicked his wand.

The lights went out. Shadows crept up the walls. At the centre of the classroom, light shimmered into an illusion, unfurling in the shape of a countryside village. Thatched roofs, crooked fences, the occasional goat looking judgmental. The sound of chickens clucking drifted in faintly, followed by laughter and the clink of pots.

A girl knelt by a well, scrubbing something. Her sleeves were rolled up, hair pinned messily, face flushed from sun and effort.

Cassian gestured at her. “This is Eliana.”

Her voice floated through the air, nothing fancy, just her calling for her mum, asking if they were out of soap again.

A few students blinked. Daphne leaned forward, eyes narrowing slightly.

The girl straightened. Across the lane, a young man, shirt half unbuttoned, wand tucked behind one ear, was chopping wood in no particular rush. He looked up. Their eyes met.

“And this young, dashing lad,” Cassian said, “is Illyius.”

Someone near the front let out a hmm, and Tracey whispered something that sounded suspiciously like “Wait a second—”

Hermione leaned forward, eyebrows already at high alert. “That looks like—”

She turned sharply. “Aren’t those Professors Babbling and Rosier?”

A few students snickered. Cassian didn’t blink.

“Coincidence,” he said flatly. “Must’ve been a handsome century.”

In the illusion, Eliana handed Illyius a bucket. Their fingers brushed. Neither moved away.

The classroom was dead quiet. Somewhere near the back, someone whispered something about scandal. Cassian ignored it.

“Eliana and Illyius were from a mountain village, half-magic, half-mud, whole lot of goats. Life was small. Predictable. They were happy with that.”

The illusion shifted. Same village, different day. Eliana was laughing at something Illyius said as she handed him a broom handle longer than she was tall.

“Until a dark wizard named Raczidian decided he fancied himself a bride.”

The air cooled. The scene flickered to grey. A dark-robed figure stood outside the village, surrounded by things that looked like Dementors.

“He sent a letter. Flowery nonsense. Promised power, gold, a bloody keep. Eliana said no. Her family backed her.”

The torches dimmed further. The dark figure raised one hand.

“So he sent his friends instead.”

The scene twisted. Smoke poured from the edges of the illusion as the village screamed to life. A few villagers cast protective charms. A handful even managed a Patronus, flickering and frail. But there were too many of them.

“Dementors didn’t care about loyalty. Or family. Or love.” Cassian’s voice didn’t change. “They wanted warmth. And this village had a lot of it.”

“People fell. Memories bled out of them like spilled ink. Children collapsed mid-run. Whole lines of defence flickered and died because no one had the strength to hope.”

The room was still. Even Malfoy had shut up.

“Then Illyius stepped forward.”

Cassian froze the illusion mid-battle, smoke paused mid-whirl, villagers half-collapsed, Illyius reaching out with his wand, and turned back to the classroom.

A few students blinked like they’d just been yanked out of a dream. Tracey looked personally offended. Dean muttered something that sounded suspiciously like, “You’re joking.” No one laughed.

Cassian, however, felt zero guilt.

“Right. Believe it or not, if you grow up in the mountains, you either learn this charm or you don’t last the winter. But! Until that point,” he said, flicking his wand to brighten the torches again, “the Patronus was more myth than method. People used it against dark creatures, something passed down in scraps. Picture the light, feel something good, hope for the best. Something to ward off the evil spirits.”

He leaned a hip against the desk, scanning the class. “No structured spell. No theory. No proper wandwork. Bit like giving someone a bow and arrow and telling them to hit a dragon.”

He tapped the board with the end of his wand. “Anyone here know how to cast one?”

Hands shot up, Daphne, Tracey, Pansy.

Cassian waved them off. “Nope. Told you before. Doesn’t count.”

The girls groaned in unison. Pansy flopped sideways over her desk dramatically.

Cassian turned away from the theatrics. “Anyone else?”

Neville hesitantly raised his hand.

Cassian pointed at him. “Go on, Longbottom.”

Neville shifted in his seat. “U-um… you need to think of a happy moment. One really strong memory.”

Cassian nodded. “Correct.”

He stepped away from the desk, crossing to the front of the class again. “That’s the start, yes. Patronus is fuelled by memory. Not just any memory. The right one. Has to be warm enough to stand up against the cold that sucks out everything else.”

He glanced across the rows. Most students were watching now.

Cassian pointed at the frozen illusion hanging in the air. “Now the thing is,” he said, “when something that ugly’s trying to suck the soul out of you, it’s really bloody hard to focus on your happy place. Shocking, I know.”

A few students gave weak laughs. Most just nodded.

“Right. But that’s the point. Life doesn’t pause and give you time to meditate when it kicks you in the teeth. It just keeps going. So you either drown in misery, or you latch onto the one thing that doesn’t hurt.”

He motioned to Illyius, wand raised mid-spell in the illusion, frozen in that breath between action and disaster.

“Illyius was losing everything. Friends, family, the only home he’d ever known. And in the middle of all that, he thought of Eliana. Her laugh. The way she looked at him like he wasn’t just some lad with a crooked wand and goat dung on his boots.”

He raised his wand. “And that was everything to him.”

The lights flickered, and the illusion snapped back into motion.

Illyius braced his feet, wand gripped tight. Then…

Light.

A sharp burst of light leapt from Illyius’s wand. A mouse, tiny and silver, shot out of the wand’s tip, tail streaming behind it like a whip of light. It sprinted straight across the burning illusion-village, weaving between the houses and dodging falling embers. Then it turned, teeth bared, and launched itself at the first Dementor.

The shriek it tore from the creature made two students flinch in their seats. Pale, skeletal limbs flailed as the light slammed into its face.

Another Dementor reeled back, trailing dark mist like torn fabric. The Patronus darted again. The shadows didn’t so much retreat as flee.

Within seconds, the Patronus had cleared a space around Illyius. The other villagers, still collapsed or barely standing, blinked against the sudden warmth pushing back the cold. One or two started to move again.

Cassian let the illusion run for a few seconds more, then gave his wand a flick. The scene froze. The mouse stood mid-bound, tail curled in mid-air, jaws wide.

He turned back to the class.

“Illyius didn’t come from some noble house. He didn’t study advanced defence theory. He wasn’t even particularly powerful.”

He pointed at the frozen Patronus.

“But he loved her. And that was enough.”

No one moved.

Cassian sighed and leaned back against the desk, crossing his arms.

“And before anyone asks, yes, it was the first confirmed corporeal Patronus in recorded history. And yes, the officials ignored it for another sixty years because they didn’t like the mouse.”

Pansy raised her hand halfway. “Seriously?”

He nodded. “True story. Too small, apparently. Not flashy enough. Someone actually wrote a paper calling it ‘undignified animal symbolism.'”

Dean muttered, “Bet that guy couldn’t cast one himself.”

Cassian smirked. “He couldn’t. His own notes admitted it.”

That got a few snorts.

Neville raised a tentative hand. “What happened to Illyius and Eliana?”

Cassian shrugged. “Lived. Married. Built a new house further up the mountain. Five kids. One of them became a Charmwright. The others mostly raised goats.”

Pansy blinked. “That’s it?”

“What were you expecting? Tragic death? Bit of Shakespearean misery?”

She opened her mouth, paused, and then gave a small nod. “I mean… maybe.”

Cassian gestured at the frozen scene again. “Not every hero dies. Some of them get old and grumpy and yell at chickens.”

Bulstrode raised a hand. “Sir, if Patronuses are tied to memory, do they ever change?”

His eyes slid to her. “They can. If you change enough, the Patronus usually follows.”

Ron frowned. “What does that mean?”

He tilted his head. “Think of it like a reflection. If you’ve been through a storm and come out the other side with different bones, the mirror’s not going to show the same face.”

Daphne looked thoughtful. “So, if your form changes… does that mean your memory changed too?”

“Not always,” Cassian said. “Sometimes the memory stays the same. You just see it differently.”

The class was quiet again.

Behind him, the mouse Patronus still hovered in mid-leap. A tiny, furious spark of light in a village otherwise scorched and dark.

Cassian tapped his wand once more. The illusion dissolved into mist, fading like breath on glass. The torches flared back to life, returning the room to its usual warm glow and chipped stone.

He glanced at the clock. Still a few minutes left.

“Right,” he said. “I’ll talk about Azkaban and why Dementors are parked there like moody seagulls later. For now…”

He waved a hand vaguely, like he could physically fling the next words away.

“This is going to sound like the hippiest thing I’ve ever said, and I’ve said some real rot…” he paused, pulled a face, “but the only way to fight darkness is love.”

That got a full-body shudder out of him. He shook his hands like he’d touched something sticky. “God, that was awful.”

A ripple of laughter passed through the room. Someone near the middle actually applauded. He ignored them.

“But it works. Annoyingly.”

He turned, started writing on the board again. This time in blocky letters.

HOMEWORK: 3 FEET ON YOUR HAPPIEST MEMORY.

A few groans. Pansy immediately dropped her head on the desk with a muffled, “Why are you like this?”

“You lot keep asking that like it’s going to change anything,” Cassian replied.

He underlined the words with a sharp flick.

“Write them out in excruciating detail. No vague nonsense. I want smells, sounds, feelings. Not ‘we had cake,’ but what kind of cake, and why it mattered. Think about what happiness actually feels like. Why that moment stuck.”

He glanced over the class again. Tracey had already pulled a roll of parchment onto her lap. Hermione looked like she was ready to draft a thesis. Ron was half-asleep with his eyes open.

“Bonus points if you can define happiness,” Cassian said. “Not a dictionary quote. Yours. What it is. What it means to you.”

He leaned against the edge of the desk, arms folding lazily.

“And then you save that memory. Bottle it. Keep it tucked somewhere in the back of your sleeve. Because one day, maybe not next week, maybe not this year, but someday, something might try to take it from you.”

He paused.

“And when that happens, I want you to have something sharp enough to stab it in the face.”

The bell rang. Chairs scraped. Bags shuffled. He waved a hand vaguely at the lot of them.

“Off you go. Try not to die before next lesson.”

Pansy passed him on the way out and muttered, “If mine turns out to be a goose, I’m quitting school.”

Cassian didn’t look up. “Not before I mount it to the classroom.”

(Check Here)

It is funny really, your presence is constant, yet your impact feels hypothetical.

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