A/N: This is based off a prompt I got in a role-play from ages ago, it's been edited a fair bit from the original. I hope you enjoy!
Christmas Eve, 1970
Andromeda's eyes wandered carelessly to the mirror over the fireplace, which was held in an elaborate frame encrusted with semi-precious stones. In the mirror, she caught sight of Narcissa and Bellatrix walking out of the ballroom, standing close enough to each other to be able to speak without being overheard and watched the oak door with the mirrored back panel close behind them.
Christmas Eve, 1959
House-elves were going about setting up decorations for the annual winter ball, and everything was glittering and luminous and beautiful. The three girls were hanging tinsel, Andromeda standing on a stepladder to reach the top of the Christmas tree.
In the beginning, Christmas had been widely accepted by the Wizarding world as a silly, muggle holiday, pointless to celebrate and only of worth to muggle-lovers. This stereotype still held, to a certain extent, as most of the Wizarding elite refused to refer to their winter balls as "Christmas", but rather as a celebration of the more traditionally-observed winter solstice. Still, elements of Christmastime had slowly begun to creep into the old pureblood families, the Christmas tree being the more obvious of them.
There was a loud crash, recognizably the sound of breaking china- in this case, Druella Black, who had just sent a porcelain ornament clattering to the ground. "I will not have this," she hissed, pointing an accusatory finger at Cygnus Black, who stood opposite her. The sisters had stopped hanging the tinsel, their eyes shifting to the brewing fight between their parents. Cygnus had grasped Druella's right upper-arm, and started to direct her outside the room, the oak doors closing hard behind him. She was struggling slightly, unwilling to follow his lead. They never fought in front of the children, even though that hardly meant that the children never knew they were fighting. Their voices were raised. Andromeda hated it when they fought. It never ended well. She could tell from the look on Narcissa's face that she hated it too. Bellatrix, on the other hand, glanced at the door with apathy unlike that of a regular eight-year old. Andromeda would later learn that Bellatrix knew that their parents' relationship had been forged for the sake of formality, for practicality, and the times when they argued merely reflected the times when they cared to show how they truly felt about each other.
Eventually, Andromeda perched herself on the top of the stepladder, looking into the mirror on the top of the fireplace.
"Bella," Andromeda had said. "Bella, Cissy, look." She had scooted over on the stepladder, motioning to Bellatrix and Narcissa to come join her. Andromeda looked into the mirror on top of the fireplace, pointing at it as it reflected the mirror on the back of the closed oak doors. The mirror showed the three of them, reflected a million times, maybe even more. "We're going to be like that," she had declared. "We're going to be together forever and forever and forever, no matter what happens."
Bellatrix had laughed, pulled her and Narcissa close when they had gotten off the ladder and assured her that they would be together 'forever and forever'.
But those were promises made by children, and a war held no place for the vows of the naive.