*Supposedly takes place during first season
The setting sun faintly grazed the hills of Ponyville, another day of joy and delight. While most ponies would set off to retire for the approaching night, a group of friends thought otherwise.
Outside of Sugarcube Corner sat a yellow mare. Seated on a bench, she pondered her day. Her friends had all gotten together for a party, hosted by the one and only Pinkie Pie. She enjoyed the company of her best friends, something she never expected to have. But during the midst of the party, she had wandered off. The atmosphere of a party was overwhelming; she needed time alone, but a certain party-goer thought differently.
“Hey Fluttershy!” Pinkie exclaimed, having finally found her. “I’ve been looking all over for you. You’re missing out on all the fun!”
“Oh, um, hello Pinkie,” Fluttershy anxiously responded. Silence suddenly filled the air.
“Uh, Fluttershy? I said you’re missing out on all the fun.”
“That’s okay. I’m alright. You can go back now, no need to have me to enjoy yourself,” Fluttershy stuttered, desperately trying to avoid eye contact.
"What! How could we possibly not include you?" Pinkie mimicked her, backing Fluttershy into the seat. “You sure you’re alright? You don’t look alright.”
"Yes, I'm completely okay!" She quickly blurted out; beads of sweat slowly formed.
Noticing the distress in her voice, Pinkie halted her advance. "Okie-dokie-lokie!" she said in her normally bubbly voice. Not wanting to push further, Pinkie decided it was best to leave her alone. Trotting away, she stated "But if you need anything,”—Pinkie looked back with concerned eyes—“know that we're here for you." Knowing Fluttershy, it would take a while for her to open up, so she hopped on back to the party, hoping a while wasn't too long.
Fluttershy sat there, panic taking hold of her mind. Nothing was making sense. She became completely unsure of what terror had resided within her. Normally she wouldn't lie to her friends or even hide from them. Even though she knew her friends were there for her, she avoided Pinkie’s concern. Knowing not what came over her, she did the only thing she knew how to, run and hide.
~
Pinkie entered Sugarcube Corner as if nothing happened. The party atmosphere still filled the air. Confetti, streamers, and other party decorations were sprinkled about, and the rest of the party conversing. Noticing the arrival of the party host, her friends started to ask her questions.
"Pinkie, where's Fluttershy?" Twilight inquired.
"Did ya find her?" Asked Applejack.
"Is she okay?" Rainbow added.
"Please do tell us if something is wrong, darling," Rarity stated.
Overwhelmed by the questions, Pinkie started to nervously laugh. "Yeah... Uh, she's fine; she just wanted to... Take care of the animals!"
Rainbow began, "Isn't that –"
"Why don't we have some more punch, or play more games. Like... pin the tail on the pony!" Pinkie rushed back and forth between the kitchen and the main room to bring back party supplies. "Or – maybe – you – guys – would – rather – dance?" Beginning to hyperventilate, Pinkie stopped to take a few breaths, laying down on the floor.
"Pinkie, is there something bothering you? We can all leave if we have to," Twilight suggested.
"But the party just started!" Protested Rainbow, receiving scolding looks from the others.
"No, no, no, no. You guys don't have to leave. It's fine, no need to worry. See”—Pinkie made the biggest smile possible—“everything is a'okay."
Either deciding it was best to not press further or writing it off as a 'Pinkie' thing, they stopped questioning her. They all knew something was wrong, but didn't want to harass Pinkie over it, so they continued partying, if it could even be called that anymore. Silence consumed the room; everypony became lost in thought.
~
The end of the party finally came and as always it was time for farewells. One by one the ponies began to leave.
"That was one heck of a shindig, Pinkie. Thank ya kindly for having me, but I better get on home and rest up. Them apples don't buck themselves," Applejack waved goodbye and galloped off.
"Yes, this was quite the party. However it is dreadfully late and I simply must retire for the night. Again, as always, thank you for the delightful party," Rarity bowed as she bid her farewell.
"This was fun and I can't wait to do this again, but I have to continue my studies. Remember to invite me to your next party!" Twilight said before cantering off.
With three ponies gone, two were left, and the last one was not about to leave without answers.
"Um, Dash, don't you have to go home?" Wondered Pinkie.
"I do. But first, I need to know what was going on," Dash stated.
"What do you mean?" Pinkie started to look away. "Nothing was going on. Just a normal party."
"Pinkie please. Don’t avoid the question, just tell me…" Rainbow lowered her voice and sighed, "Look I know something is wrong; I just want to help. Fluttershy is my best friend; we’ve known each other since fillyhood. And when something's wrong, I know there is."
Pinkie surveyed the room, making sure there were no watchers. Content with the results, she exhaled, her eyes fixated on the floor. "That's the problem... I don't know what was wrong with her. I left her hoping she would come back.”—Sniffles broke her speech—“But... she didn't." Drops of sadness fell to the floor. “Are my parties really that bad?”
Seeing Pinkie in such a state of sadness was rare. The once cheerful, outgoing pony, reduced to a statue of grief. She felt abandoned, unwanted.
Rainbow sighed and quiet mumbled to herself, “Fluttershy… why?” Not wanting to see Pinkie beat herself up over this, she went over to comfort her. Helping her off the floor, she tried to reassure her: “Pinkie it’s okay.”
“How is it okay?” she somberly relayed, facing away from her. “She left without saying goodbye. Did we do something wrong? Maybe she hates us or even thinks we’re not good enough for her or e–“
“PINKIE. There is no way Fluttershy would hate us. She just…”—Rainbow stopped to ponder—“Just… This has to be a misunderstanding.” Rainbow turned Pinkie to face her, “Please, Pinkie. Tell me what happened.”
Pinkie stared on through her, “She was scared.”
Rainbow looked at her with annoyance, “She’s always scared.”
“Not just scared, scared. She panicked. Like, tried to avoid me, as if I was a stranger.”
Rainbow beckoned her to continue.
“I mentioned the party and she started to panic."—A revelation struck her—"Does she hate my parties? But who could hate parties? Did something bad happen to her at a party?”
"Hmm. Fluttershy never was one to be a socializer, but she seemed okay with my parties back then. I would always invite her, hoping she would try to make new friends. However, she always just stayed near me."
"What does that have to do with my parties? It was only us six."
"I don't know..."—Rainbow pondered on her old memories—“She always seemed happy to go to my birthday parties."
"Did you ever go to hers?"
"Yeah—wait a second. I don't ever remember her ever inviting me to one..." Rainbow saddened at the thought. "I don't even know when her birthday is."
Gasp "You mean she's never had a birthday party before?!? That's terrible! Everyone should have a birthday party. This is an emergency, we have to throw her a party pronto."
"Woah, woah, woah. Hold on there Pinkie. I don't even know"—Rainbow expression widened at the revelation—"I never asked when her birthday was… Ugh, some friend I am!" Rainbow stomped her hoof repeatedly against the floor, each with increasing force. "Stupid, stupid, stupid! All those years of forgotten birthdays… How could I have never asked her? We say we're best friends, but the only real friend is Fluttershy. I've spent too much time thinking about myself that I never even knew… I have to make this up to her. I don't care what I have to do. I just have to,” Rainbow held her head down, "Do I even deserve the title of loyalty?"
"Dashie… Don't say stuff like that. You do deserve it; you're already wanting to make up for your mistakes."
"But how am I going to make it up to her?"
"Start with an apology. Maybe we can throw her a makeup birthday party for all the ones she missed."
"Yeah," Rainbow started to lighten up, "That's a perfect idea! It can even be a surprise party."
"Sounds good to me. But let's plan it tomorrow, it's pretty late and this talk was”—Yawn—“emotionally draining."
"Okay, I'll be back early in the morning," Rainbow said, dashing off, barely containing her giddiness.
"Okie dokie”—Pinkie drops dead—“loki..."
"Just you wait Fluttershy, we're going to throw you the best birthday party ever. The one that you deserve."
Author's Note
Ugh, what a terrible story.
But in all seriousness, thank you for reading I guess.
I had ideas for stories all the way back when I started following the show back in 2011, but never wrote them because I hate myself. Anyways fast forward a bit... I began writing this 4 months ago... and this is just the first chapter, of my first story... Yeah... I'm such a procrastinator 
Anyways if you have any suggestions on how I can improve this story or writing in general, it would be much appreciated.
Once again thank you for reading my garbage writing.