Author's Notes: Written for Prompt #311 on femslash100 on Livejournal – "Smooth".
"I'm not going to let you do this to me," Andromeda said simply.
Bellatrix's eyes flashed, and she dropped her hands from where they had been caressing her sister's hair, face, body. "What?"
"You think you're perfect," Andromeda said, sounding bolder than she felt. "You think you can wrap anyone around your little finger, because you're just that smooth, don't you? Well, you're wrong. You're not. And I'm not going to let you stop me from doing what I want. And don't you dare pretend I can't!" she added. "I'm not letting love – sisterly or… otherwise… get in the way."
"I'm not supposed to love you like this," Narcissa sobbed. "You're my sister! I'm supposed to love you like a sister, the same way I love Bella, but I don't! I… I…" She looked up at Andromeda with her pale eyes streaming teary trails down her cheeks.
"Shh…" Andromeda ran her fingers gently Narcissa's silky hair, then smoothed her hand over her brow. "Don't cry. I love you too… it's going to be all right, darling."
"Really?" Narcissa whispered, her eyes full of tears as she looked up at her big sister.
"Really," said Andromeda, and then added, "I promise."
"You're mine," Bellatrix hissed, and Narcissa resisted the urge to swallow hard as the icy smooth blade of her dagger pressed against her throat. "Mine, do you hear me? Not Lucius's, I don't care if you're married to him!"
"Y- yours," Narcissa whimpered, echoing her sister as she had learned to do.
"And you'll never love anyone as much as you love me, isn't that right, Cissy?"
"Good," Bellatrix breathed, lowering the knife. "Now give me a kiss, Cissy, to prove that you love me."
She trembled, but nodded and kissed her sister anyway.
Because she loved her.