The silence after Cassius' vow lingered like incense, thick and heavy, until the owl's rustle of wings broke it.
Noctis settled on the desk, golden eyes gleaming, watching as if she too knew the weight of the pact just made.
Grindelwald leaned back in his chair, a weary smile tugging at his lips.
"So eager, so certain. You remind me of myself. That is both your greatest strength… and your most dangerous flaw."
Cassius said nothing, refusing to be baited.
Instead, he asked the question that gnawed at him.
"If you knew your revolution was doomed, why decide to go into exile? Why this prison? Why not simply… coexist living free as the defeated party?"
The old man's mismatched eyes glittered.
For a moment, he looked almost amused.
"Coexistence, boy, is just a polite word for surrender, and after what i had done, the world would not accept me to live, it was only albus, and albus alone who would grant me the mercy of life, but at the cost of staying here until the world forgot i existed. I could not walk among them as if my cause had never burned. They would have demanded my life in exchange for those i had claimed, but i had a reason to live, i had you to meet."
"Then why remain here? Travel around free but away from the muggles and magical habitations?"
At that, Grindelwald grew serious.
His hand, veined and brittle, reached for his staff.
He tapped its silver knob, and faint sparks danced.
"Because Albus demanded it."
Cassius frowned.
The old man chuckled softly, shaking his head.
"You think me here by choice alone? No. At the end, when our duel was finished, he forced my hand. A new blood pact was wrought, carved between us in fire and pain. I swore—no, was bound—not to take up the revolution again. Not to raise wand or word toward the dominion of wizards over muggles. My hands are shackled, boy. Not by these walls, but by the pact, i could leave yes, but if i did so, it would almost be guarenteed i would die in the attempt."
Cassius' eyes narrowed.
"Yet here you are. Speaking of visions. Calling me heir."
Grindelwald's smile sharpened.
"Precisely. The pact binds me… not you. I cannot lead the revolution, but nothing forbids me from teaching. You are the loophole the pact did not account for, or perhaps the loophold intended within it. My silence ends the moment another voice carries the song."
Cassius felt a thrill crawl up his spine.
A chain broken, not by defiance, but by cunning.
He could almost admire the irony of it.
"So, you will train me."
"Yes. But first, I must know what clay I shape."
Grindelwald gestured for him to sit.
"Tell me of your blood. Your roots. Your... world."
Cassius sat stiff-backed, folding his hands before him.
"My mother was Lily Evans. Pure-blooded by lineage, though her family was cast out centuries ago. Squib-born Slytherin descendants. Her magic reawakened with her. My father—Severus Snape. Half-blood. His mother, Eileen Prince, came from an old pureblood line. His father was… muggle."
Grindelwald listened intently, nodding once.
"Three-quarters blood, then. Strong veins, though not uncontested. You are a child of castoffs and survivors. An interesting alchemy."
Cassius nodded to Grindelwalds words, throughout the Fanstastic Beasts arc Grindelwald never claimed to hate muggles, nore the muggleborn, magic in general was the blessing regardless of who had it.
"I walk between both worlds," Cassius added. "Muggle and magical. I've seen their ignorance, their arrogance. Both sides blind, both sides brittle to what lay before them."
The old man's smile returned, thin and knowing.
"Yes. And that is why you are dangerous. You carry in your bones what most wizards refuse to admit: that muggles are not cattle. They are a threat. But threats can be… redirected, guided if you will."
Cassius felt heat in his chest.
Validation.
He'd spoken such thoughts to no one, not even himself fully, and here they were met not with scorn, but with recognition.
"Then teach me to bend them," he said quickly. "Teach me to make the wizarding world rise."
Grindelwald raised a finger.
"Patience. First comes foundation."
He rose slowly, robes trailing as he crossed to a shelf.
From it, he drew a stack of parchment bound in leather straps.
He dropped it onto the desk before Cassius with a dull thud.
"A curriculum," Grindelwald said. "The training of a revolutionary is not forged by wandwork alone. Magic is easy. Understanding is hard. So your first lessons will be theoretical."
Cassius' face soured.
"Theory? You would waste my time with reading while the world festers?"
The old man's chuckle was low and cutting.
"Ah. Impatience. Always impatience. Do you think battles are won by spells alone? A child with a wand can hurl fire. A fool with knowledge can kill by accident. But a leader—a leader must know why wars are fought, what binds men to causes, what breaks nations into submission."
Cassius bit back his protest, but his fists clenched.
Grindelwald ignored it, continuing as though lecturing to a hall.
"You will study magical law. Muggle history. Economics—both worlds, mind you. The alchemy of symbols, the runes of old Europe, the ways empires rise and fall. Philosophy of war: Sun Tzu, Clausewitz, and the hidden grimoires of our kind. You will know bloodlines, alliances, betrayals. Only then will you learn what spell to cast, where to strike, whom to kill. Otherwise, you are just another boy with a wand, doomed to die screaming like the rest."
The words stung, but Cassius could not deny their truth.
Still, frustration burned in his chest.
"And what of dueling?" he pressed. "Of hex and curse? What if I am attacked tomorrow?"
Grindelwald's mismatched eyes glittered with amusement.
"If you are attacked tomorrow, you will die tomorrow. Better you learn that now than feed yourself fantasies. You are clever, but untested. You cannot outfight a grown wizard yet. Your power lies in not being seen. In watching, learning, and preparing. Theory will keep you alive long enough to wield practice."
Cassius' jaw tightened.
"So I am to sit and read while the world spins on."
"You are to sharpen your mind until it is sharper than any blade." Grindelwald leaned forward, voice hard as steel. "Fire without form is just smoke. Form without fire is just stone. You must be both—flame and vessel. If you balk at study, you are not worthy of command."
The rebuke hit Cassius like a lash.
He wanted to argue, to demand spellcraft, to prove himself more than parchment and patience.
But a deeper instinct held his tongue.
Grindelwald's eyes were not mocking.
They were measuring.
Testing.
Slowly, Cassius inclined his head.
"Very well. I will learn."
Grindelwald's smile returned, almost indulgent.
"Good. Already you show more sense than half the fools who once followed me. They hungered for glory, for duels, for blood spilled quick. And they burned fast. But you—"
He tapped Cassius' forehead lightly with a crooked finger.
"You might just last."
The fire in Cassius' chest simmered, controlled now, not extinguished.
He hated the thought of waiting, afterall inside he was almost 30 years old, not enjoying being treated like a child and told to wait.
He hated theory without action.
But deep inside, he knew the old man was right.
Patience was another form of power.
Grindelwald sat back once more, voice softer now.
"We begin tomorrow. For tonight, rest. Read the first volume—'The Architecture of War.' Think on what it means that muggles conquered half the world not with spells, but with ships, guns, and paper."
Cassius rose, clutching the tome as though it were both gift and burden.
His owl shifted on the desk, feathers rustling, as though sensing the weight of what was to come.
As he turned toward the door, Grindelwald spoke once more.
"Remember this, boy. Magic without knowledge is chaos. Knowledge without will is dust. But together… they are destiny."
Cassius paused, spine straightening, and answered in a voice that no longer sounded entirely like a child's.
"Then I will master both."
Grindelwald's chuckle followed him into the stairwell, a sound like fire crackling in the dark.
"Good. Very good."