This is user envy34's fault, I couldn't sleep and they suggested this crossover over in 'The Lady of Slytherin' so here you go, long short for new readers, The-Girl-Who-Lived was raised by Snape, Sirius, and the Black Sisters, we'll consider this an alternate ending to that story. Anyway enjoy the madness Lillith/Lelouch is going to be kinda fun to write.
The Lady of Slytherin Lilith Dorea Potter-Black-Peverell was not in a particularly good mood at the moment, in fact she'd go insofar as to say she'd passed the realm of 'a bit cross' and had firmly camped in 'Fucking Infuriated'. One minute the Dark Lady of Britannia was in Tokyo enjoying a rather tasteful expose on Japanese culture on her first holiday since toppling the corrupt Ministry of Magic and the next she found herself face first in the ghetto. The memories leading to this event cluttered and clashed in the young woman's mind, most of it some macabre tableau that made very little sense to her and all she could clearly recall was a caricatured symbol of a bird in flight.
Brushing her exquisite dress robes clear of any dust the ravenette woman narrowed her almond shaped emerald eyes in consternation, this entire city looked like it needed hit with a scourgify charm...or an air strike. Flicking the charms hanging off her bracelet she realized their connections to all her friends and minions were dead, grumbling in irritation she pulled the Elder Wand from her purse and began to gingerly walk around the debris strewn street.
"No Hermione, no Draco, no Blase, no Dad, no Sirius, no Auntie Bella...this is just great..." lifting her shimmering ebony skirts Lilly hopped across a pot hole while not for the first time regretting her choice of heels for the evening...or early afternoon now if the sun was any indicator. Mulling over that little caveat The-Girl-Who-Lived blinked rapidly as she saw a several meter tall...robot...yeah giant fighting robot smash through a rotting building wall and open fire on a group of children. After pulping their tiny bodies into chum and ichor the machine spun on its axis and sped away firing away on some other unfortunate innocents.
Now, Lillith had done some rather...severe and questionable things in her short tenure as the Dark Lady, filling the vacuum left by the deaths of Dumbledore and Voldemort simply left her little choice in some matters. That being said, slaughtering fleeing groups of children, muggle or magical regardless was just something that rubbed her wrong and tweaked the bit of her core that was an abused and neglected little girl. Apparating before the machine Lilly cast a dark cutter on the violet and black behemoth tearing its legs out from beneath it, as the tumbling wreck rolled to a stop before her she sat primly on a bench waiting for the pilot to exit.
As things stood she didn't have to wait long for the battered hump on the machines back to split open disgorging a coughing young man, standing up she sauntered up to the pilot as he was gasping incoherently into a headset. Tapping him on the shoulder he spun around trying to bring a pistol to bear as she jammed her wand into his temple while hissing out, "Legillimens," as she violated the mans mind the Dark Lady felt her mild headache grow into a full blown migraine.
"That's...lovely...the mother isles fell to Napoleon, Holy Empire of Britannia, conquering the world for the laughs...that's...ugh..." Staring at the trembling man a moment she sneered in a manner that would make her adoptive father proud as she spat out "Avada Kedavera!" With a seekers reflexes Lilly snatched his pistol from his limp grasp as the dead body fell to the ground and began walking towards the sounds of war echoing from deeper within the ghetto, "Hermione's right, this saving people thing really ruins the entire 'Dark Lady' persona...gonna have to work on that..."
With that thought she found a massive pile of dead bodies strewn about the street as if just common chaff, finding her rage crystallizing the whites of her eyes turned obsidian black as her iris's glowed a scintillating green. Cutting her palm she let her blood fall to the ground and began incanting an ancient Sumerian rite, after a few moments the dead bodies all began to stand shakily. Smirking she switched to parseltongue,
"Tear apart those that murdered you, magic for magic, blood for blood, life for life," nodding as one the dozens of freshly minted inferni shambled before her in search of meat, if nothing else this should prove entertaining.
Kallen Kozuki was honestly at her wits end, their simple snatch and grab operation on Prince Clovis' weapons development facility had devolved into a high speed chase through the ghetto of Shinjuko, a massacre of innocent civilians, a near rote against Britannia thanks to a mysterious benefactor, than everything went to hell when that White Demon showed up. Seething that she had to abandon her stalwart Glasgow Kallen was guiding several civilians away from the fighting when the far wall collapsed .
Both she and Ohgi froze in horror as they stared down the Britnnian APC, over a dozen soldiers wielding automatic rifles were poised to open fire on the defenseless group. Kallen felt the lump in her throat harden as the smirk of the officer turned into a sneer and he began to give his command the order to fire,
"More Eleven filth, men op-" he was cut off by the rattle of weapons fire and the screams of the dying, the soldiers all turned to see pale faced corpses with bone clawed fingers and slavering jaws swarm over the group baying for blood. Several of the civilians threw up as they watched these ghouls devour their would be attackers, not skipping a beat once the last soldiers quit moving the ghouls moved on not even giving the buildings occupants a second glance. The automated turret on the APC began to turn and lock onto the undead when several explosions riddled its side, after a moment it exploded sending debris flying.
As the refugees and freedom fighters tried to process the carnage before them Kallen recognized a whistled tune,
"Is...is that In the Hall of the Mountain King?" She asked her shaken mentor, before he could respond the source of the whistling, one Britannian woman who couldn't be any older then herself skipped before the burning APC. She spun sending her black skirts fluttering as she giggled out,
"And maybe next time you won't screw with the bitch witch with the itch for the snitch!" Still staring dumbly none of them moved when the crew door blew out and a soldier stumbled through the billowing smoke of the ravaged wreck, the woman pointed a stick at the man and in an incredibly bored tone stated, "Reducto." The unfortunate grunt was reduced to viscera and bone shards as his mortal remains sprayed against the destroyed war machine, turning to finally acknowledge the group the Britannian woman smiled widely.
"Brilliant! Could you lot possibly tell me where this Prince Clovis bloke is? I gotta a cruciatus to pick with him..."