(A/N: This is for the Marauder's Era Challenge in the Harry Potter Fanfiction Challenges forum. I do not own Harry Potter, obviously. She's better at writing than this.)
Bellatrix had always teased Narcissa. She loved to taunt her youngest sister; to pull her blonde hair just so, until Narcissa invariably burst into tears and Bella tried to look innocent.
"Look at you, you cry-baby," Bellatrix would whisper again into her ear, once the suspicious parenting eyes had turned away. "Haven't you ever wondered why your hair is so freakishly blonde and ours isn't, Cissy? Why you have such a weird name, when the rest of us are named after the stars?
"You're not really part of our family, Cissy. You were adopted. I remember—I'm the oldest. I remember when somebody just left you on our doorstep, and Mother and Father decided to take you in. You might not even be a pureblood. You could just be some filthy Muggle off the streets."
They were ridiculous claims, of course, because Narcissa resembled several extended family members, and the Black family would never have adopted a Muggle child, even one left on their doorstep; and in fact, Narcissa usually performed some kind of accidental magic whenever Bella upset her with these claims. It was a testament to the terrifying conviction with which Bella spoke, however, that Narcissa always believed her.
Many years later, when people began to whisper about the things that Bellatrix was capable of doing with the Cruciatus curse under the Dark Lord's tutelage, Narcissa hardly batted an eyelash. She had been Bella's first victim long before the Cruciatus curse came along.
Andromeda was as different from her sisters as could be, though she still shared the same darker (Black, ha-ha) beauty that Narcissa lacked. Where Bellatrix was passionate, and Narcissa was cold, Andromeda was warm: It was to Andromeda, not to her mother, that Narcissa would run after she finally got loose from Bella's grasp. In her middle sister's arms she would collapse, crying, while Andromeda soothed her and told her that her hair was not freakish, it was beautiful; and that she wasn't adopted, just different.
While Bellatrix constantly strove for something beyond her family and beyond Hogwarts, pushing herself into the Dark Lord's inner circle, Andromeda and Narcissa remained as close as ever. Instead of crying in Andromeda's arms about her oldest sister, Narcissa would cry about boys, and the gossiping girls at the school, and the way her professors looked at her when she did something wrong.
"I'm ugly." Narcissa would sob. "I'm stupid, and I'm horrid, and I'm going to end up an old maid, or-or married to a stupid Mudblood or something."
To which Andromeda would softly kiss her little sister, repeatedly, and whisper, "Don't be silly, Cissy; you're beautiful. I've always told you that."
And Narcissa believed her, too, more than she believed Bellatrix, more than she believed the Dark Lord's claims about blood purity and what needed to be done. Despite Bella's passion for the Death Eater society, Narcissa never particularly cared about any of it. Of course she thought she was better than everyone else, but that was just because she was a Black, not because of her pureblood status.
It was that stupid Ted Tonks who changed her mind.
Ted —what a stupid, Muggle name. He was the one who ruined everything—who stole Andromeda away, who made her say that she was in love, who made her say that she couldn't stand to be with her family anymore, who turned Narcissa's lovely, agreeable sister into some unrecognizable creature who went against her family, against her heritage, against her house to run away with him.
Everyone in the pureblood community said that it was such a shame, because all three girls had come from such a respectable household. Horrified and angry as Narcissa's parents were, nothing matched Bellatrix's fury when she discovered Andromeda's treachery. Narcissa went along with it, too, disowning her sister just as the rest did.
Everyone assumed that she did it out of similar anger that her sister would leave and marry a Mudblood. Everyone assumed that Narcissa felt wounded that her sister would betray the Black family. Nobody ever suspected, least of all her family, that Narcissa's rage was that Andromeda would leave her; that Andromeda would betray her, when Andromeda had always, always been the one to take care of her little sister.
She hid the pain well; nobody ever knew that Narcissa Black—later, Narcissa Malfoy—missed her sister at all. They did not wonder at how protective she was of her son, how she refused to send Draco to a far-away school and about the lengths to which she went to protect her family once they had fallen from the Dark Lord's favor. They did not wonder at the ease with which she betrayed the Dark Lord in the final battle against Hogwarts. To the end, Bellatrix never knew that Narcissa's loyalty was only a pretense.
It was only after the battle of Hogwarts had ended, when Bellatrix was dead and her family was safe, that people looked up in wonder to see Narcissa Malfoy walk into her niece's funeral and embrace her older sister as she grieved. For the first time—after more than twenty years—it was Narcissa's turn to comfort.