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The first time they meet, he is eight and she is six. They greet each other appropriately, stiff and formal in their charmed clothes and look each other in the eye as their parents plan their future above their heads.
The next time they meet, Narcissa has just been Sorted into Slytherin - with a less time than it takes to blink under the Hat's brim. Remarkable, even for a Black. He meets her gaze and rises to applaud her.
They meet occasionally in the Slytherin Common Room - but never for long. She's always surrounded by a giggling gaggle of her friends and he is always with his.
Neither of them date anyone in Hogwarts. The Malfoys aren't yet quite important enough to afford to get on anyone's bad side, and the purity of a Black daughter is too easily broken to be cast into even the faintest shadow of doubt. They know their own value.
They meet at night, a few years later, in a session of Muggle-torture, where she is oblivious to his presence but where Lucius is most certainly not oblivious to hers. He falls in love with the sweep her wrist makes just before she casts the Unforgivable, with the swirl of blonde hair that winds its way free of the dark hood, with the harsh flash of green in the blue eyes behind the mask, with the way she holds her perfect position for half a heartbeat before moving on. He sees that everyone else's hems are spattered with mud and blood, but there is not a single drop of anything on her pristine black robes.
They are permitted, mow that Narcissa is seventeen, to meet a few times, chaperoned, in the gardens of Malfoy Manor. Lucius sees the glittering blue eyes and her long blonde hair and quietly falls in love all over again.
Narcissa has doors opened for her, has her chair pulled out, has her glass refilled, enjoys a summer afternoon of good company and good conversation and thinks that marriage wouldn't be completely awful.
Narcissa thinks she's in love a month before her wedding day, when she sees her ring and her clothes and the long, long guest list; line after line of wealthy, influential people with hundreds of powerful connections of their own. Here is the exact reach of The Noble And Most Ancient House Of Black, laid out in ink and parchment in front of her eyes.
She thinks there is not a more satisfying sight in the world.
Her marriage into the Malfoy family will only serve to increase the influences of both families. She will have a household of her own. She will be answerable to no one - save her husband. She doesn't think this is an entirely bad thing. He seems to be kind enough. He is, after all, providing her with a means to become as independent as she ever will be.
The guests pay their respects to the couple and comment on how well they look together. The excellence of the connection. The superior quality of the food and drink compared to anything they have tasted in their lives. How happy they look.
She doesn't really fall in love with him until two weeks into their marriage. They're out on a Muggle-torture session again, and Narcissa is slapped by one of the Muggle men before she can turn her wand on him. She is frozen in shock for a moment; she has certainly been slapped before, but never by such a dirty, filthy creature. She looks up at her husband and falls in love.
Lucius does not look fazed; not while the man is whimpering for mercy under his mere stare, not while the man is screaming under his Cruciatus, not even when his voice has given out under torture curses Narcissa has never even heard of.
He kills the man in the slowest, most painful way possible. Nobody has ever done this for her before - nobody has ever had to, for a start. It is strange, to be sure, but it is an oddly touching gesture. When the man is dead, Lucius strides over to where Narcissa is standing, cups her chin and brushes her bruised cheek with his thumb to ease the discomfort as he mutters a charm and heals her face. She is entranced by the look of utter calm in his eyes and the muted anger behind them.
He brings her a new set of jewellery the next day - necklace, earrings, bracelet - with diamonds and sapphires to match her eyes, and emeralds and onyx to match their favourite colours - and fastens the necklace as she lifts the curtain of her heavy blonde hair for him. It ought to be a great ugly thing, with so many stones and so much silver and gold everywhere (she thinks it might be white gold, or platinum, but he doesn't say and she doesn't ask), and yet the stones are so perfectly cut that it is a delicate thing of fragile beauty, and it is utterly beautiful. He meets her eyes in the mirror.
She's more of a Slytherin than he'll ever be, even after all these years. She'll switch sides in an instant, if it will save her son and her husband. And it did. And he finally realised that, bowed his head and acknowledged what she had done to save his name and his soul from Azkaban and the Dementors.
In the end, she loved him for that above all else; for his pride and his humility; for his strength and his weakness; for his independence and his attachment to his family. She thinks it is the adversity that makes the true human; that it is the failure that makes a man; that it is the emotion that makes the Slytherin woman; that it is the flaws that make a flawless human being.
It takes the longest time, but he comes to agree.
They fell in love amidst the screams of the innocent, the smells of burning flesh, the heart-stopping green flashes of light. They smiled and tortured and killed, safe behind their faceless masks and fell in love while they did it. They fell in love as they ripped apart the lives they held at the tips of their wands.
Theirs is a fairytale written in blood.
A/N: I was intrigued by the idea of Narcissa embodying that characteristics of Slytherin better than Lucius does - cunning, ambition, etc. Going to Snape behind Voldemort's back? Saving Harry's life in public view of the Death Eaters and Voldemort himself? Yes, I think the woman's got a spine of steel, whereas I think Lucius Malfoy is a fool. I was interested in Lucius falling in love with her first, rather than the other way around.
The Noble and Most Ancient House of Black vs. the Malfoys? Yes, I think that the Blacks had a much higher standing than the Malfoys - and that is only reversed because there is no Black brother to carry on the name. And so the Malfoys take up the reins - due to the connection through Narcissa, the only Black that is not dead, estranged or in Azkaban.