Sirius Black prided himself on two things:
His unmatched talent for making Remus Lupin sigh in exhaustion.
and his belief that pranking was an essential form of wizarding self-expression.
So naturally, hosting six teenage girls, his godson, and his childhood nemesis under one roof did not, in any universe, deter him.
If anything, it emboldened him.
By the first true morning of the holiday, Sirius was stalking the halls with the scheming energy of a man preparing for war.
~
In the private lounge on the third floor—Black family-only territory—Sirius slammed a stack of parchment onto the table.
"Gentlemen," he announced, puffing his chest out as if addressing a Wizengamot assembly, "we have a problem."
Remus looked up from his tea.
Snape didn't bother looking up from the potion journal he was reading—a new edition detailing Arcanum released concoctions.
Sirius gestured emphatically at the ceiling.
"Cassius has lowered his guard."
Remus gave him a look. "He's surrounded by six girls. That's not lowered— that's suicide."
"Exactly!" Sirius declared triumphantly. "And therefore—prime prank time."
Remus groaned.
Snape exhaled slowly, closed his journal, and fixed Sirius with the ocular equivalent of a Killing Curse.
"You dragged me up here… to propose pranking my son."
"Yes."
"You mean my highly competant, disturbingly perceptive son, whom you've been in a pranking war with for close to two years and have never gotten even a single leg up on?"
"Yes."
"Who last year had gotten to you so hard, you almost feared what it would mean becoming a professor at Hogwarts and having to continue facing him year round?"
"Yes!"
Remus sipped his tea. "Sirius, Cassius is going to kill you."
Sirius grinned wildly. "Not this time, i've got the perfect plan!"
Silence.
Snape stared.
Remus stared.
Even for these men who stood on opposite ends of the spectrum, in this moment the pair found themselves as almost kindred spirits staring at the third man in the room.
~
Somewhere downstairs, a cabinet exploded.
Likely Luna trying to find the "singing teacups."
Sirius leaned forward.
"Just picture it. Cassius, all calm and collected, surrounded by his girlfriends like some miniature Dark Lord in training—and BAM!—a harmless, tasteful prank hits him square in the ego."
Snape pinched the bridge of his nose.
"I cannot believe you are my own son's godfather..."
Remus nodded. "None of us can."
Sirius pointed at them both. "I need allies. Moony, for practicality. Snape—"
"No."
"—for ruthlessness."
"No."
"—and because Cassius would never expect it!"
Snape's eye twitched.
Remus muttered, "Sirius, you cannot honestly expect things to go well can you?"
"Do they need to go well? The whole point of pranking is, simply to do it for the sake of doing it, blow off some steam, get a laugh. Grab a few photo's to remember and bring up at every opportunity!"
Snape finally being fed of with the two got up and left, but as he did, he heard the two behind him continue to talk.
"He never said no, that means he's interested!" came Sirius's words.
Honestly Severus did not want to participate, but getting more involved in Cassius's life... even if it was only joining a prank war... well that didnt sound to bad.
Let's see if his own son, could do worse than the quadret of villains he had to endure throughout his school life.
If the old dog couldnt teach him new tricks, perhaps a fresh perspective was required.
~
Meanwhile, Cassius's morning was much more dignified.
He walked his assembled council—six girls of very different temperaments—through Grimmauld Place like a young lord showing off a palace built from shadows and secrets.
Daphne absorbed everything.
Astoria followed with awe.
Hermione asked an unending stream of questions.
Cho listened politely and with grace.
Ginny seemed shocked half the time and enthralled the other.
Luna simply drifted along like she already knew every hidden corner.
Cassius led them not to the familiar rooms, but to the hidden ones.
The Black Family Spell Archive—rows of magic that was brilliant, ancient, and occasionally homicidal.
The Hall of Ancestral Portraits, who bowed to Cassius with eerie, dignified approval, not initially but after exposing his magical powess and bloodline as a technical pureblooded wizard they softened enough to agree him the heir to house black until Sirius produced a direct heir that is.
And lastly…
The sealed door.
Black marble.
Silver veins.
The crest carved deep enough to radiate magic.
"The Black Council Room," Cassius said.
This room was previously a dungeon in the basement, but in the year since he was accepted here, Cassius had remodelled the room into his very own inner sanctum.
The room itself housed many of his secrets, the room being the current abode of his alter ego Nyx.
Ginny blinked. "You have one of those?"
"All great houses do," Daphne answered quietly. "But most families abandoned the tradition centuries ago."
Cassius placed his hand against the door.
Dark magic shimmered—accepting its master.
The door opened.
~
The room was circular.
Torches burned with blue flame.
A round obsidian table lay at the center, carved with protective runes and old oaths.
"This," Cassius said, "is where the head of House Black meets with his chosen. Advisors. Allies. Inner circle."
Daphne's eyes gleamed.Hermione's breath caught.Cho bowed her head with respect.Ginny's cheeks flushed at the honor.Astoria clung to her sister, overwhelmed but proud.
Luna hummed. "Feels like a good place for secrets."
Cassius nodded.
"Exactly."
He sat.
They followed.
Like King Arthur and his round table the seven were gathered round the round table easily able to see one another, with none officially having a higher station.
Those who sat closer to cassius might be seen as having an advantage but those further away got to look him directly in the eye rather than needing to turn to see.
With a flick of his wand, the torches dimmed, shadows drawing closer.
"For Christmas," Cassius said softly, "I want to give you all a gift. Something personal. Something private."
The girls glanced at each other, a few even burning bright crimson as their thoughts got ahead of themselves.
"It's only fair," Cassius continued, "as i'm sure Lady Draconis has explained, i as the head of house must likewise trust in all of you."
Hermione leaned forward. "Cassius… you don't have to—"
"I do."
Only causing all of them to burn crimson now, unaware of the nightly talking session the girls had with the aforementioned Lady.
He looked each of them in the eye.
Sirius might have been joking upstairs.
Snape might have fled the room earlier.
But down here?
Cassius was no child.
He was a young lord baring his truth.
"My mother," Cassius began, "is Lily Evans."
The reaction was immediate.
Hermione gasped.
Cho's lips parted in shock.
Astoria's eyes widened.
Ginny froze.
Daphne's expression sharpened like a blade.
Luna blinked once—slowly—as though confirming something she'd already suspected.
Cassius continued quietly.
"She was married to James Potter. During which time she also had an affair. Which resulted in my own creation..."
Hermione whispered, "Merlin…"
The revelation of his now exposed heritage had rocked the room.
Aside from the people involved no one else knew of this secret.
Up until now Lily was even a respected professor in their eyes, but with this grand reveal it finally made sense why Cassius had made his recent move, if you found out the truth, that you had been abandoned by the woman who bore you.
Only to then find she also took up post at the castle to be near her real son, but was neglecting her duty as a professor in the process, none of the girls oculd find fault with his actions.
Even endorsing them after the fact.