Author's Notes: Warning for sibling incest and underage.
It's exciting to slip out of her own bed and into her sister's, she discovers. Her heartbeat seems to treble, her body trembles in its virginal white nightgown, as she peels away the blankets and molds her body to Bella's. Across the room, Andy pretends to be asleep, as she always does, although Narcissa would wager that Andy's fingers are down her knickers and her eyes are half-open.
"Cissy," Bella hisses in her ear as she hikes up her younger sister's night-dress, only to discover Narcissa isn't wearing anything underneath. "Naughty girl," Bella whispers in appreciation. Narcissa bites her bottom lip and nods, excited anew. They must be quiet, so very quiet, or else Mum or Father might come in and catch them, but Cissy doesn't mind being quiet. Not for her older sister. Not for Bellatrix.
It's happened so long. Another family tradition that's tucked away in a drawer with the lavender-scented handkerchiefs and the clothes all three girls have outgrown. A secret like what happens when Father drinks too much, or the way Mother's tongue loosens when she's overly tired. It's part of being a Black, and Narcissa is proud to be a Black, proud to be Bellatrix's sister.
They exchange too-long glances over the breakfast table, Bella helping Cissy fold her napkin, fingers brushing over the delicate skin of her wrist just a fraction too long. Father laughs and calls them silly children, but the glint of knowing in Druella's eyes makes Narcissa's mouth dry, makes her heartbeat as frantic as the flutter of a hummingbird's.
But Mother says nothing, and life goes on, because it is the family way, and when Cissy slides into Bella's bed at night, she knows that it's where she belongs.
"I love you, Bella," Narcissa whispers, her hips bucking against Bellatrix's questing fingers, like they always do, and her cry is swallowed in Bella's bruising kisses.
Bellatrix says nothing as Cissy lies next to her, panting, but then again, she doesn't need to.