Rainbow Dash had stuck around long enough to discover that Mercury would be going out with her friends to celebrate. Judging by their insistence, they would probably be out for several hours.
She had never felt a fury quite like this before, and she wanted to share her negativity as best she could. The anger had blinded her of all goals but one; she wanted to hurt this mare. She wanted to damage her, break her, something to quell this uncanny rage she was feeling.
Rainbow Dash stormed into the pegasus district, located the house of her new-found nemesis and, with a short running start, flew straight into it.
Airborne houses, being made of cloud, were naturally pervious to pegasi. In order to prevent break-ins and vandalism, the cloud used to make most buildings was generally heavily reinforced and densely-woven, making it impossible for the average pegasus to pass through them. Rainbow Dash was not an average pegasus. Under the onslaught of the enraged ace flyer, the walls may as well have been cirrus.
Dash broke through the wall into the main room, and began looking around for something to break, some way to hurt her enemy.
The house was sparsely decorated. The living room had only one small table, one chair, and a small couch, none of which matched. One wall was adorned with numerous medals and plaques celebrating Mercury's racing prowess.
Dash walked over to this and, with a wry grin and a broad stroke of her hoof, knocked some dozen trophies to the floor.
It wasn't enough. She wanted to hurt Mercury, somehow. She moved deeper into the house.
She came upon a small, messy room with a bed. Jackpot. She immediately began rummaging through everything, grabbing whatever she could get her hooves and and chucking it all over the room: laundry, books, magazines, sheets, trash. In the midst of the maelstrom she wrought upon the room, the bed was shoved hard aside, revealing a small box labeled "Top Secret." Hello, what have we here?
After stopping for only a brief moment to examine the box, Dash brought it on top of the bed and opened it, spilling its contents all over the sheets.
"Oh..."
She shook her head, and grinned evilly.
"Oh, this is good."
The most striking of the contents were the dozen-or-so magazines tucked inside, bearing titles such as Fillyfoolers Anonymous or Marefriends Illustrated. One of these had fallen open, revealing a spectacularly R-rated scene featuring several mares in congress.
Homosexuality was not necessarily frowned upon in modern Equestria—quite the opposite, actually—, but it still wasn't normal. Something like this could be devastating to a pony's reputation. If Mercury was gay—and that was a small if, thought Dash as she flipped through one of the magazines, in which some pictures had been crossed out, others circled, a few brief lines quips of adoration written here and there—, then this would be the perfect ammunition for Dash to shoot her down with.
She shut the magazine and placed it back in the box, shifting her attention to the only other item of note within the box: a small leather-bound book that could only be a diary.
She picked this up and turned to a random page.
Well, Leafy did it again. She said she'd stop, but I guess something got the better of her. I went over to her house—she was supposed to pick me up today, and I assumed she'd just overslept again. I found her passed out in the kitchen. There was a syringe on the counter, and she was hardly breathing. I don't know why she keeps this up. This stupid shit nearly killed her before, and now she's right back here on the floor, choking on her own spit. What would she do without me, I wonder. What would I do without her?
Well, thought Rainbow Dash. That explains that weirdo, I guess.
This is like a goldmine. She turned to the latest page, bracing for whatever tale of angst and woe awaited her there:
Recently, I won second place in the Ponyville Final...
Oh boy. Dash mused.
But I hate it.
Rainbow Dash raised an eyebrow.
I hate racing so goddamn much. I hate going too fast and losing control, I hate crashing, I hate the pressure, I hate the competition, I hate the attention. I hate it all so, so much. But, alas, racing is my life.
As Rainbow Dash read the emotional tirade about the life of an unwilling racehorse, she felt the burning rage inside of her give way to something else, something warm and bittersweet, not unlike pity, flavored with no small degree of regret.
And then this mare, Rainbow Dash...
Dash winced. Here it comes. Dash wanted to wilt away there, hang her head and curl up until she just vanished. But she kept reading.
...a rematch? She won. What does she want a rematch for? I certainly don't...
Slowly, with tears burning in her eyes, she forced herself to finish the entry.
It's bullshit how she's too damn proud to see through my friends' boasting...
She forced herself to endure as, line by line, each word sent through her a pang of... guilt? Dash had once inadvertently knocked another racer off-course, sending him off into a wall and injuring him significantly, then standing by awkwardly as he was carried off on a stretcher, to the horror of his attending family and friends. This felt similar to that: a feeling of dread and guilt, tainted with doubt. It wasn't her fault. She was just doing the same thing she always did. So what if somepony else screwed up?
...it's bullshit that I'm going to have to race her all over again. It's bullshit that I even stand a chance against her...
Yes, it was.
I want nothing to do with this, but what could I possibly do to back out?
Dash shut the journal and stormed out of the room, not looking up as she marched out of the house.
A visibly-inebriated Mercury touched down in an open square near her home in the pegasus district, followed closely by her stunted green friend.
"Y'sure ya don't need me to walk you home? You hit that sauce pretty hard."
"Nah, 'm good."
Mercury had drunk a lot. It was one of the only ways she knew to deal with stress. And she was stressed. She had won the race, sure, but now she was afraid. Dash had been furious, it seemed, and she feared what she would do. She had hit Leafy, after all, so she was clearly not very much in control of her actions. Was she the sort to hold a grudge? Would she want to hurt Mercury?
These thoughts clouded Mercury's already-hazy mind as she turned down the road to her home, slurring goodbyes and parting ways with her friend, walking with her head down. Her mind cleared almost instantly, however, when she heard yelling from further down the road.
"And just what do you think you're doing?" shouted a voice that was ineffably calm despite its volume and apparent anger. Mercury looked up, and saw that the yelling had come from a yellow pegasus with a pink mane, reprimanding none other than Rainbow Dash.
In front of her house.
Part of Mercury wanted to duck into an alley or fly away or anything to just disappear right then, but Rainbow Dash had already noticed her. She began approaching Mercury, her head hung low.
She mumbled something.
"Come again?" said Mercury.
"I'm sorry."
"What? It's fine. You lost your temper, I get it. It's—"
"No, it's not. I didn't know. I'm sorry."
"Didn't know what?" Mercury asked, looking slightly worried.
Dash hung her head and remained silent.
Mercury stared at her for a short while, and then headed inside. Dash followed her.
Mercury's breath caught when she saw the torn-up wall of trophies, but she did not react further. She walked over and regarded it more closely, kicking at some of the fallen medals. She wore a sober face, like she had been expecting this to happen.
"I'm sorry." Dash repeated.
"Don't be."
Rainbow Dash looked up, puzzled. "What?"
"I... I don't care. About this."
"I can help you clean, if you want. I can..."
"No." Mercury cleared a spot on the floor and sat down, then began sifting through the debris. "Don't. This is... okay." Her voice was quiet and fragile.
Dash approached and sat quietly behind her. "Can I do anything?"
"No, I'm just... tired of this. All of this... this dumb bullshit."
Rainbow Dash cocked her head. "What do you mean?"
In response, Mercury stood up and knocked the remaining medals off of the wall, then fell to the ground, crying.
"I don't want this! I don't want to ever race again. I just want... I don't know. I'm sick of racing."
"Oh." Dash stood and helped Mercury to her feet. "I'm sorry. I don't know what came over me. I thought that maybe... I felt like you were trying to hurt my pride or something, and I... didn't know how to deal with that? I wouldn't have... if I'd known that you... I'm sorry. I'm so sorry."
Mercury sniffled, and then embraced Dash in a tight hug and began even harder. "All people think of me is 'race this, race that' and I don't give a shit! I have no interest in doing it, but nobody would ever dare think that because I'm so fast that... I just don't want to..."
Mercury released Dash, turned around and began walking towards her room. When she saw inside, she gasped, not at the mess that had been made of everything inside, but at the "Top Secret" box atop her bed, and its incriminating contents strewn across her sheets.
Her dull, sombre attitude was supplanted by a sort of desperation, and she turned to Dash. "Did you look?!"
"I didn't know. I'm sorry."
It was Mercury's turn to hang her head. "Just... just don't tell anypony. Okay."
Dash blushed and looked awkwardly away. "Yeah." She smiled timidly, then held out a hoof. "Friends?"
"I... " Mercury said, looking at first stern and then contemplative. "...why not." Mercury extended her own hoof. "Friends."