Harry Potter and the Surprisingly Competent History of Magic Professor

Cassian's breath hitched.

The moment he focused on the name, something cracked open in his mind.

Not memories... at least, not his. Something older, alien. Images stabbed through his mind, cold and jagged, like glass splintering behind his eyes. A dark forest, thick with mist that clung to his skin like cold sweat. Shapes shifted between the trees... too fast to follow, too silent to be alive. Blackened, elongated limbs moved with unnatural grace. Eyes like endless pits stared back… not glowing, but drinking in light, swallowing it until nothing remained.

Around them, the air itself seemed to shudder. Shadows spilled outward, pooling like oil, suffocating the faintest glimmer of light. Stars winked out one by one above the treetops, and even the moon grew dim, its pale glow strangled as if unseen hands were snuffing it from the heavens.

The magic here wasn't mere darkness. It wasn't night, or shadow, or anything natural. It was deeper... wrong. It pressed in, heavy and absolute, an endless suffocation. Each breath came harder, thinner, as though the air itself had been bled dry. And beneath it all came sounds... bone snapping like brittle twigs, the wet tear of flesh, and something else… a low hum, almost inaudible, vibrating in his teeth.

Cassian's heart slammed against his ribs. It felt like death approaching... not the clean inevitability of time, but something hungrier, a devouring force that would leave no trace of him behind.

Cassian flinched, yanking himself out of it. The room spun for a second before settling.

He let out a slow breath, gripping the edge of the table.

Alright. That was horrifying. Also new, but mostly horrifying.

His fingers twitched. He glanced at his wand.

He knew better than to try it here. Whatever the hell Lumos Noctis was, it wasn't a party trick.

Still, a cold feeling curled at the base of his spine. Not fear.

Just the sharp awareness that something had shifted.

Something had changed.

And he wasn't sure if it could be undone.

Cassian took a slow breath. "What the hell was that?"

No answer, obviously. The room was as quiet as it had been a moment ago, the only sound was the faint crackle of the fireplace. He rolled his shoulders, trying to shake the lingering unease from whatever the hell that was. The second spell was still there… Lumos Spectaculum.

He focused on it, expecting another weird vision. Instead, images formed in his mind, smooth and clear, like flipping through a book he hadn't realised he'd read. Scholars, illusionists, teachers… people weaving light into shapes, using it to tell stories, record history, even recreate battles in shimmering detail. No creeping dread this time. No black-eyed creatures lurking in the dark.

Cassian exhaled, pressing his fingers against his temples. Alright. So apparently, he could now pull ancient magic out of thin air. Lovely. That wasn't concerning at all.

A knock at the door. Not hesitant, not impatient… just the usual get your arse moving sort of knock.

Cassian straightened. "What?"

His father entered first, his mother following close behind. Regulus clapped a firm hand on Cassian's shoulder, his expression a rare approval and relief.

"That was well done, son!" he said, nodding. "I knew you wouldn't humiliate us."

Cassian arched a brow. Not exactly a glowing review, but from Regulus Rosier, it might as well have been a standing ovation. Son. The word landed heavier than it should've. The man in front of him was technically his father now, but it was like hearing a stranger claim him. He fought the instinct to flinch, instead leaning into the performance.

"Didn't have much of a choice, did I?" he said, shaking off Regulus's grip with a casual roll of his shoulder. "If I tanked that, I would be out on my arse before the ink dried on my disownment papers."

Regulus chuckled, but there was a glint in his grey eyes. He wasn't just pleased Cassian hadn't embarrassed him… he was thinking. Planning.

Brilliant. That was probably worse.

"Perhaps you are not as entirely useless as you've spent your life proving," Regulus mused, stepping past him to pour himself a drink. "You managed to hold the room. Even the pure-bloods were listening. That is a rare talent, Cassian. Persuasion."

Cassian snorted. "More like they were too shocked to leave. Thought they'd been tricked into a remedial class."

"Regardless, it worked." Regulus took the nearby glass, then took a slow sip. "Your ability to explain magic, even something as simple as Lumos, held their attention. That is valuable."

Valuable. Right. Cassian could practically hear the wheels turning in his father's head. There was always a use for things in Regulus's world. Money, power, reputation… everything was leverage, including people. And now, somehow, Cassian had made himself leverage.

Ophelia, who had been standing near the door with her arms crossed, finally spoke. "Pity you couldn't muster half that effort back when it might've mattered," she said, her tone as dry as an empty cauldron.

Cassian turned to her, flashing a sharp grin. "Ah, but Mother, if I had, you would be out of excuses to act disappointed in me."

Her expression didn't so much as twitch. "You assume I need an excuse."

Regulus set his glass down with a soft clink, giving Cassian a long, assessing look. "I will arrange a teaching job for you at Hogwarts."

Cassian blinked. "You will what?"

Regulus didn't repeat himself. He simply held Cassian's gaze, as if daring him to argue.

A laugh bubbled up before Cassian could stop it. "Oh, that is brilliant. Absolutely bloody brilliant. The school that chucked me out because I couldn't manage first-year spells… now you want me teaching there? You remember that I graduated with a lot of favors, right?" He gestured vaguely. "What, exactly? How to disappoint your entire bloodline before thirty?"

His mother exhaled sharply, adjusting the cuffs of her robes like she would rather be anywhere else. "Language, Cassian."

"Right, sorry. Wouldn't want to scandalise the fine, upstanding Rosier name with my vulgarity." He turned back to Regulus. "But, seriously. What the hell makes you think anyone at Hogwarts would let me within a mile of a classroom?"

Regulus didn't even blink. "Dumbledore has been more open to outside hires. And your cousins won't stop complaining about how dull History of Magic is with that ghost. I believe you could make it interesting."

Cassian almost laughed. Seriously? History? Again? In this life, too? He barely wrapped his head around the fact that he was in a magical world, and now he got his job back.

"Right, of course," he drawled, slumping into a chair and stretching his legs out. "Because I am such a respected academic. What, exactly, do you think I would be teaching them? How to dodge responsibility and disappoint their parents?"

Regulus ignored the sarcasm, swirling his glass before setting it down with a soft clink. "You held their attention today. That is more than most of their professors can manage."

"That is because they were waiting for me to humiliate myself."

"And yet, you didn't."

Cassian's smirk twitched, but he kept his expression loose. "You sound almost impressed, Father. Careful, you will ruin your reputation."

Regulus didn't look amused. "You will take the job," he said. "It will give you status, and it will put this family in a position to shape the next generation of wizards. I always thought that mind of yours would get you killed before it amounted to anything, but today, you proved me wrong."

Cassian let out a slow, exaggerated exhale, slumping further into his chair. He flicked his fingers in a lazy mock toast. "So, what now? I pack my bags for Hogwarts and pretend I have a clue what I am doing?"

Regulus sat back, fingers tapping against his glass. "You wouldn't be the first."

Cassian snorted. "Comforting."

Returning home after the festival, Cassian pushed open his bedroom door and slumped into the chair by the window. His head hit the backrest, eyes shutting for a moment. The fresh breeze did little to ease the exhaustion settling into his bones. He pulled it off… somehow. Against all odds, he hadn't humiliated himself in front of half the bloody aristocracy. His father hadn't ripped into him, and Damien hadn't gotten his victory laugh. But instead of relief, all he felt was a dull sort of emptiness.

A quiet pop snapped him out of it. A house-elf stood by the door, small hands wringing together. The creature barely lifted its head, voice trembling.

"Do you wish anything, Master Cassian?"

Cassian blinked, rubbing a hand over his face. He glanced at the elf, Towel, wasn't it?, and shook his head. "No, I am fine. Thanks."

Silence.

He glanced up. The elf was staring at him, mouth slightly open, eyes wide with something between awe and terror.

Cassian frowned. "What?"

Towel flinched and quickly shook its head. "N-Nothing, Master Cassian!" It bowed so low its long ears nearly touched the floor.

Cassian squinted at it. That was the second time tonight an elf had reacted like he just grown a second head. The first had been before the lecture, when he apologised for startling one.

The longer he looked at Towel, the stranger it felt. The thing was still shivering, its hands clenched so tight the knuckles had gone grey. Cassian didn't get it. Sure, elves were skittish, but this was different.

The unease tightened in his gut. He didn't want to, but he reached into the memories of the other Cassian… the one who belonged in this body before him.

A flood of images hit him like a punch to the teeth.

Kicks. Punches. The sound of bones cracking. A twisted laugh. The sight of an elf curled on the ground, sobbing, while Cassian… no, not him, the old Cassian, loomed over it, a stick pointed like a weapon.

Cassian swallowed, throat tight.

Bloody hell.

This bastard.

No wonder Towel looked like it was waiting to be skinned alive.

His stomach turned.

What a bastard.

His fingers curled into the armrest, jaw tightening. He wasn't a saint, but this? This was pathetic. Kicking around creatures that couldn't fight back, who flinched at the mere sight of him?

Towel still stood there, visibly shaking. Cassian forced his expression into something neutral, though it took effort.

"You can go."

The elf hesitated, eyes darting up to meet his before snapping back down. Then, with another pop, it vanished.

Cassian exhaled, running a hand through his hair. Fucking brilliant. He was stuck in the life of a sadistic little shit with a reputation worse than his magic. He leaned forward, elbows on his knees, staring at the rising moon.

The sight did nothing to take the edge off.

Sleep didn't come easy. His body was exhausted, but his mind kept circling back to everything… the lecture, the spells, the weird thing floating in his head, and now, the delightful discovery that the old Cassian had been the magical equivalent of a rich kid who set ants on fire for fun.

By the time he actually drifted off, it felt like barely a minute had passed before knocking jolted him awake.

Cassian groaned into his pillow. "Go away."

The knocking didn't stop.

He peeled an eye open, glaring at the door. "For fuck's sake."

Dragging himself up, he swung his legs over the bed and shuffled over, yanking it open.

The door swung open, and there stood Lucian. He barely spared Cassian a glance before stepping inside, exuding the same effortless authority he always carried.

"Grandfather wants to see you," he said, his voice clipped. Then, with a quick up-and-down look, his lip curled. "Freshen up. And wear something decent for once."

Cassian rubbed a hand down his face, still groggy. "Brilliant. Just what I needed first thing in the morning. A family reunion."

Lucian didn't bother acknowledging that. He just stood there, waiting, like he fully expected Cassian to crawl out and obey.

Cassian rolled his shoulders with exaggerated sluggishness. "You know, if you ever got cursed into a mirror, you would make an excellent dressing assistant. Maybe even land a job."

Lucian didn't rise to the bait. "Be ready in ten." He turned on his heel and left without waiting for a response.

Cassian shut the door, exhaling through his nose. Grandfather wanted to see him. That couldn't mean anything good. Magnus Rosier wasn't the sort to waste time, and he certainly wasn't the sort to call for Cassian unless there was a very specific reason.

And if Lucian's presence was anything to go by, this wasn't just about the lecture.

Cassian dragged himself to the washbasin, splashing cold water on his face. The mirror above it reflected back the same tired, half-irritated expression he always wore around family. He ran a hand through his hair, trying to make himself look somewhat presentable, then grabbed a set of robes that weren't completely wrinkled.

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