A/N: Where this story started and where it finishes are both places I sort of had in mind when I got the prompt, but how I connected them was not at all what I expected to happen until they got written. As always, I don't own the Potterverse.
"That's what you get?"
Parvati turned at her best friend's voice, holding up the rather frilly red dress to herself.
"You don't like it, Lav? I thought it looked all right in the mirror."
Lavender Brown, self-proclaimed fashionista of Gryffindor, rolled her eyes and grabbed the dress out of Parvati's hands. "Parv, I want you to do something for me. Hold out your hands, and measure one of these frills for yourself. Then, take that measure, and see just how far away from your body this dress is going to push everyone. I guarantee you won't like the answer you get." Tossing the dress onto a small pile of other choices of Parvati's that she had rejected, Lavender waved over a salesperson. "My friend is having serious trouble finding a new dress. I still have to find one for myself, so please, help this poor girl out for me." She slipped the salesperson a 20 pound note and whispered "Get her into something spectacular, and there's another tenner in it for you at the end."
As Lavender went off in search of her own dress, Parvati slumped into a chair. The salesperson started pulling dresses off the pile Lavender had rejected, and held them all briefly next to Parvati, before putting each over her arm. "You know, dear, you seem to be looking at a bunch of dresses that don't really work with your body type. Can you show me the section you've been looking at?" Parvati led the salesperson over to the dresses she had been choosing from, which caused a shake of the head from the woman with her. "Oh my, dear, is this the section you've been in the whole time? No wonder you've been having trouble, these are the dresses for younger girls, not beautiful women such as yourself and that friend of yours. Here, let me show you something, and see if you don't think it's a much better fit."
The salesperson brought Parvati over to a section on the opposite side of the store from where she had been looking, and pulled a few dresses off the racks seemingly at random. She motioned to Parvati to stand in front of a mirror, and began holding up her selections for Parvati's approval. The first, a pale yellow lace dress, clashed rather spectacularly with her, and immediately got tossed aside, with only a muttered "Whoops" from the salesperson. The second, a rather sheer green number, got a look of incredulity from Parvati, and was also quickly discarded. The third, a backless dark blue outfit, was not immediately rejected, but still drew a look of some trepidation from Parvati, and was set gently aside, just in case.
The fourth and final dress was a shimmering, strapless silver dress that ended just above mid-thigh on Parvati. She held the dress up to herself, and after a nod from the salesperson, snuck into the changing room to try it on. After returning, the salesperson stood Parvati on a small box so she could walk around her and give a few small tugs to make sure the dress was perfect. Once satisfied, she looked into the mirror, and got an excellent look at Parvati's stunned face. "Yes, dear, that is you. I've been working here for a while, and trust me, I've yet to see anyone who looks as good in that dress as you do right now. It's as though it was made to fit you specifically."
Parvati turned slowly, so she could see the dress from all angles, but there wasn't a doubt in her mind that this dress would be going anywhere but with her then and there. A pair of shoes in the same color completed the ensemble, and Parvati had just gotten her purchases over to the counter as Lavender walked up, her own choices already bagged up. "Found something we liked, did we?" she said teasingly. Parvati was only able to blush and nod, but the salesperson who had been helping her winked at Lavender and smiled. Behind Parvati's back, Lavender slipped the salesperson the promised tenner and mouthed "Thanks" before guiding her friend out of the store.
A few nights later, Parvati was getting ready for a night out, when she remembered her new silver dress. She pulled it out of its box, and stood in front of her mirror, admiring again how nice the dress looked, and wondering if tonight was the night to wear it. A knock on her door and a shout of "Ten minutes!" made her decision for her.
Normally, when the friends met at the club, Lavender got the majority of the attention. However, she arrived a few minutes later than she had expected, so when she stepped inside, the first thing she saw was what seemed to be just about every male in the club fawning over a beautiful woman dressed…no, not merely dressed, draped in a shimmering silver material that teased just enough about all the right things while not actually showing too much of anything. Lavender felt herself heating up just from the sight. As she moved closer, she realized that she might have undertipped the salesperson at the store, because Parvati looked absolutely stunning in that dress. Once she made her way to Parvati's side, Parvati's face lit up with a brilliant smile, and it was as though she only had eyes for Lavender. Of course, with the pair of them seated together, they drew basically all of the male attention, but a few subtle pieces of wand work later, and they were finally able to get back to normal conversation with each other.
"So, you've been holding out on me for all this time? You look amazing, Parv," said Lavender. Parvati flushed, which Lavender thought just made her best friend look even better. "Whichever one of these fine gentlemen ends up going home with you tonight is gonna be real lucky." A sharp glance from Parvati, followed by her standing up quickly, confused Lavender, even as she was pulled along.
"Good night, boys," announced Parvati loudly, "I have to make sure my friend gets home safely, and while I'm sure I could trust any of you to help her" (a round of wolf whistles answered her) "I'll be taking good care of her myself. See you later." A seductive smile on her face, she began dragging Lavender to the exit. Once outside, she spun Lavender to look her square in the eye.
"You think I got this dress to impress some drunken boys at the club, Lav? You really haven't noticed, have you?" Parvati pulled her best friend in close, then kissed her as forcefully as she possibly could. With Lavender still in a daze, Parvati dragged her back to the apartment they shared. By the time they got home, Lavender had finally regained her composure enough to be coherent again. She allowed Parvati to drag her inside, but once the door was shut, Lavender spun Parvati right back against the door and kissed her just as fiercely as she had been outside the club. She also took the opportunity to let her hands get very familiar with Parvati's dress, as Parvati's hands did the same with hers. As she finally broke the kiss, she saw the same fire in Parvati's eyes that she knew was in hers, and knew exactly where this night was going to go if she had any say about it.
"I may not have seen the signs before, but damn me if I'm not gonna act on them now. Where do we go from here, Vati?" asked Lavender, her voice dripping with undisguised lust.
Surprised (and secretly delighted) by her new nickname, Parvati gently trailed a finger across Lavender's cheek and under her chin, making sure the girl followed her as she walked past. "From here? We go to your room, where I get what I want. After that? We'll decide that when the time comes."
Lavender could look nowhere other than at the slowly retreating form of her friend and soon to be much more. "You get what you want, Vati? Then what do I get?"
Parvati stopped, slowly pulled the zipper of her dress down, and walked right out of her dress, emphasizing every movement for Lavender's hungry eyes as she entered her friend's bedroom.
"That's what you get."