"Mmmmmm, you've really outdone yourself, Trixie," Starlight commented as she took her sip of tea.
Trixie, smiling to her closest friend, took a sip of her own as she sat in her new office. "Quite. Let it never be said that the Great and Powerful Counsellor Trixie can't accommodate a guest from time to time."
Starlight sighed. "Still hard to think this won't be my office anymore."
Trixie chuckled. "Well, since you have a much better office now, I'd say you'll get used to it." The two laughed together, then took further simultaneous sips, after which Trixie sighed with contentment. "I spent a lot of time on the road, so I had a lot of free time to think of new teas to make. You'd be amazed at just how much you can brew for yourself while travelling."
Starlight rolled her eyes. "If what Twilight has taught me about Zecora's exploits are anything to go by, I think I can believe it." Then a smile came to her. "Oh! I should invite her over for a visit some time! Get her in on this tea party one day!" Then hesitation came to her. "Um, that is once she actually has a free day."
Trixie smirked. "Oh, I imagine her new role will keep her pretty busy. Ruling a whole country probably won't leave much time for breaks."
A sigh escaped the new Head-Mare of the school. "Except for her closest friends of course."
Trixie smiled to her, reaching over and giving her a quick pat on the hoof. "Don't forget, Twilight does consider you one of her closest friends."
Starlight smiled back, clearly grateful for the attempt to cheer her up. "Thanks for saying so. But honestly, I'm not sure how much time I'll be having. I mean, I knew Twilight had a lot of work running this place, but I guess I just didn't know how much."
A quick chortle from Trixie. "You're telling me. First day I took this job I had a flood of kids coming in for help. Still, nice to know Trixie is somepony they think they can confide in. There was a time I'd have never thought of myself like that."
Starlight grimaced. "Preaching to the choir on that one, Trix. Go back a few years and I'd be the last person you'd want going near any children."
A silence fell over the both of them as memories of their past poor actions began to settle on their minds. It gave a dour feeling to the tea break, no question, but it thankfully ended as Trixie once more broke out into a smile. "Well, here's to self-improvement," she remarked, holding up her cup.
Starlight, seeing that, smiled back, holding up her own cup and gently clinking it against Trixie's, after which they both gulped down what remained of their tea. After that, Starlight exhaled deeply. "Honestly, sometimes I think it's nothing short of a miracle that Twilight ever took me in like she did. All the things I did, and I still wound up as a friend to her."
Trixie nodded. "Well, I guess if you're gonna be the ruler of all Equestria, it helps if you're something of a Saint." A dry chuckle on her part. "Even if it does mean you end up befriending your deadliest nemesis."
Starlight almost seemed amused by her statement. "Huh, never been called that before. Not that you're wrong of course."
In response, Trixie seemed rather annoyed all of a sudden. "Um...pardon Trixie for saying so, Starlight...but I was referring to myself."
A pause, after which Starlight cocked an eyebrow. "...You?"
Trixie frowned. "Yes! Me! I'm Twilight's deadliest nemesis!"
Starlight couldn't stop herself any longer, and actually laughed at that, though she tried to cover her mouth while she did so. After a while, the laughter died down, but Trixie's look of annoyance remained, prompting an apologetic tone on Starlight's part. "I'm sorry, Trixie, but you're not Twilight's nemesis. I don't know if you've noticed, but she's had waaaaaaaay bigger problems to deal with than you in her life."
Trixie waved her off. "Yes, yes, big and apocalyptic monsters or national threats and all the rest of it. But I'm talking nemeses here, Starlight. Those you oppose, or are opposed by or personal reasons. And as far as that category is concerned, nopony tops the Great and Powerful Trixie."
Starlight tapped her chin. "Hmmm...you sure? Because I don't want to sound like I'm bragging or anything, but I like to think I held my own in the nemesis department."
This time, it was Trixie's turn to look amused. "Oh yeah? Trixie used an ancient artefact of dark magic to become all-powerful and force her out of her home, after which I enslaved said home and became a tyrannical dictator." She leaned on her desk, smirking to Starlight. "Top that!"
Starlight matched her smirk, leaning forward in a similar way. "Well I trapped her and her friends in my creepy cult, stole their cutie marks, then enacted a vengeance plot that almost brought about the destruction of the whole world!"
Trixie imitated a yawn. "Oh yes, very nice. But my crimes stung her far worse!"
Starlight looked aghast at such a declaration. I...but...how...how could you possibly think that taking over one single village can compare to nearly ending all life in the world?!"
A quick laugh from Trixie. "I had forced Twilight to live in a swamp to wallow in feelings of helplessness while her friends were subject to my every whim."
Brushing aside a stray strand of mane that had fallen in front of her face, Starlight remained unconvinced. "Well I had her feeling helpless when her friends were in a bad way too! Every timeline I sent her to had her friends in more and more peril!"
Slowly, Trixie clapped, but in that way somepony only did when they were clearly not impressed with what they'd seen or heard. "Oh yes, that's definitely good," she said sarcastically, then starting to look mischievous again. "But you only opposed Twilight twice. I got to her three times."
Here, Starlight looked confused. "Three?"
Folding her forehooves, Trixie had a look on her face that suggested she'd already won this conversation. "Yep. There was my initial humiliation of her during my first performance, there was my stint as a super-villain of course, and finally we had that time I tried to get under her skin by convincing you to come to my show instead of her dinner?" But then Trixie, seeing Starlight's irritated face, began to backtrack. "Um, not that I'd gloat about that last one, obviously, since it's a sore point in our long and very pleasant history as friends?"
Starlight, shaking her head, did her best to ignore the sting of that past memory. "Even if I were to count that last one, it's no good to put quantity over quality. My time as a villain was far more devastating than yours, which makes me the bigger threat. Plus, I had that whole 'powerful unicorn who had no friends' thing? You know, like some perversion of Twilight herself?"
Trixie leaned back into her chair, groaning with obvious annoyance. "Uuuuuuuuugh! Seriously? You're going for the dark reflection angle? That's so done and tired!"
"It's a classic!" Starlight retorted. "Besides, it's better than wanting revenge against somepony who didn't even wrong you to begin with!"
Trixie looked almost insulted by that. "I'll have you know that Twilight absolutely did wrong me! She drove me out of Ponyville and humiliated me!"
Starlight arched an eyebrow. "Really? Because the way I heard it you just willingly ran out of town before anypony actually did anything."
Trixie's eyes darted left and right for a moment. "Well...yes, okay, that was how things went down. But they would have turned on me eventually! My story of fighting an ursa major was proved false, so Ponyville and Twilight would have driven me out!"
Starlight stared at her, utterly baffled. "But...why? If anything they'd be mad at Snips and Snails for letting the thing loose in the town. All you did was make up a story about it. Nopony was forcing them to find a dangerous creature."
Trixie shrugged. "Hey, when has 'making sense' ever stopped anypony from doing anything in this place?"
Starlight slid down into her chair. "Well, can't argue with that one." Then, she started thinking. "Actually, now that I think on, it, Twilight seemed far less happy to see you than she was to see me back when you and I first met. I mean, I'd nearly wiped out all life in the world, yet she treated me as a close friend. But one look at you and all of a sudden it's like her worst enemy had arrived."
Naturally, Trixie looked to her friend smugly. "Told ya. Top nemesis right here."
Rather than try to counter that, Starlight scratched the back of her head. "Well...yeah, Twilight certainly acted that way."
Seeing her friend look somewhat disheartened, Trixie leaned over and patted her on the hoof. "Oh, don't let it bother you. It's actually not all that uncommon for those mares to be kinda weird with their priorities like that."
Confusion came to Starlight. "What?"
Trixie grinned. "Oh yes. Remember, Applejack is perfectly willing to be good friends with a guy like Discord who, like, betrayed them about a dozen times, but she has this total blood feud against a couple of lowly con-stallions like Flim and Flam. Bottom line, it's the small things that get under these mares' skins, not the big and dangerous stuff."
Starlight blinked a couple of times as she considered that. "You know, I actually can't deny that."
Then, much to the surprise of both of them, the door of the office opened, causing them to turn to look to see who it was that now arrived onto the scene. To the shock of them both, it was none other than the topic of conversation, Twilight Sparkle herself. And as she entered, she greeted them both with a smile, all while levitating a pile of papers alongside her. "Sorry to interrupt, but I suddenly remembered that I took these with me during my big move to Canterlot. They were supposed to stay here." A blush came to her. "Sorry if you were having trouble finding them."
As was typical with her, Trixie looked totally unconcerned with Twilight's worry. "Oh yes, we've been completely pulling our manes out looking for it," she said sarcastically.
Twilight, picking up on her tone, looked to her with a deadpan expression, then headed over to a nearby filing cabinet to drop off the papers, and Starlight, looking to her, soon stood from her chair and pointed to her. "Um...Twilight?"
The Princess looked back to her friend. "Yes?"
Hesitation was the order of the day for Starlight, but after a moment of debating whether or not to ask, she finally bit the bullet and did so. "Who...who would you say is your nemesis?"
Both Trixie and Twilight were taken aback that she'd be so forward about it, but after a while the latter began to think on the question more seriously. "Well, now that you mention it...there is one I consider to be my greatest enemy."
Instantly, Trixie looked interested, looking to her with undivided attention. "There is?! Oooooh! Do tell!"
Twilight frowned as she looked to the side. "It is one that has plagued me my whole life. One whose arrival marks great shame and trouble for me. One I wish I could be truly rid of, yet find myself having to deal with time and time again. A foe that, in the end, I may never overcome."
Both of the other mares were getting hyped now, and stepped forward together. "Yes...who is it?" Starlight asked.
Twilight, in contrast to how she'd been moments earlier, actually started to giggle, then patted the aforementioned filing cabinet and the papers she'd put there. "Oh, it's my moments of forgetfulness. You wouldn't believe how embarrassing it is for me to suddenly remember I've put something in the wrong place like this."
A long silence, after which Trixie and Starlight looked to each other with pure disappointment, with the former speaking for the both of them. "You know...what were we expecting?"
Author's Note
I love the trope of "who's the better friend" in fiction, but I think the "who's the better arch-nemesis" might actually be more entertaining to me 
