Empty space. A void filled with distant, cold lights that shed no warmth. Rainbow Dash was floating in nothingness, feeling nothing.
Pretty boring dream if you ask me, she thought. She wondered when Spitfire would show up and start taking off her soaked Wonderbolts costume; it usually happened right about now.
Oh, there it was; Spitfire was trotting this way, dripping wet and hips swinging suggestively. The fact that she was trotting in nothingness was something that Rainbow Dash failed to note. She closed her eyes, lips waiting for the kiss she knew would come. As usual, Spitfire kissed her passionately, pushing Rainbow to the ground.
At this point, Rainbow was struck by the urge to peek at her idol's face. She did so, slightly opening her eyes...
And meeting the empty black voids that replaced Spitfire's own eyes. Rainbow screamed and jumped away from the nightmare, spinning to face the thing that was imitating Spitfire. Her eyes were there, a vivid orange, but Rainbow knew the truth; this wasn't Spitfire.
Not-Spitfire hesitated, then moved slightly towards Rainbow. Rainbow stepped back to match it, growling at the thing. The Wonderbolt (fake! Dash screamed at herself) looked hurt and uncertain, and Rainbow felt sorry...
Before remembering those eyes again.
"Who are you and what did you do to Spitfire?!" she yelled at Not-Spitfire. The mare backed up, looking confused and hurt, before disappearing into the void completely. One moment, there; the next, gone. Rainbow was happy that Not-Spitfire was gone... but sad that her fantasy had been interrupted.
Just as suddenly as before, Spitfire was there, peeling off her uniform, wet mane plastered to her head. Rainbow, however, would have none of it; a flying tackle brought the two mares to the ground, Rainbow on top.
"I said," Rainbow growled, poking a hoof into Not-Spitfire's chest, "Who are you, and where is Spitfire?"
Not-Spitifre hesitated a moment. "It's me, Dash," she muttered. That voice wasn't anything like Spitfire's, and just as Rainbow processed that the mare's eyes went wide. She disappeared into the void, leaving Rainbow alone again.
"What the hay?!" she screamed. All she wanted when she went to bed was some fantasies about her idol, not confusing monsters that looked like her idol. Not-Spitfire appeared for a moment, looking apprehensive, but a glare from Rainbow made her disappear again.
This dream sucks, Rainbow thought. And suddenly, she was hit by a wave of sadness. It wasn't her own; she couldn't explain it, but... something was saddened by her thoughts, and so powerfully that it seemed to be leaking into Rainbow herself.
"Hey, uh... sorry?" Rainbow had no idea who she was talking to or why she was apologizing, but that feeling of sadness was crushing her, and she felt bad about causing it in the first place. Not-Spitfire appeared again, this time not hiding the creepy empty eyes.
"Do you... mean it?" she whispered softly.
"Of-of course!" Rainbow stammered, distracted by the empty eyes. The crushing sadness lessened a bit.
"Was I not good enough?" Not-Spitfire whispered, catching Rainbow off-guard. "Did I do something wrong?"
"N-no, it's just... the eyes..." Not-Spitfire's eyes became normal orange-colored ones, and she sighed dejectedly.
"I'm sorry... I hope you just forget this when you wake up..." the mare muttered, before turning away. The sadness Rainbow was feeling diminished, but... increased, at the same time, like it was more intense but further away.
"Hey! Wait!" Rainbow shouted at the retreating Not-Spitfire, who turned back towards her. Rainbow trotted over to the mare, hesitating a few feet away. "I'm just confused, and the eyes freaked me out. Who are you?"
"I'm..." Not-Spitfire paused, thinking. "I don't know. I change a lot. Whenever I'm close to somepony's dreams, I... change. I can hear what they want, and I try to give it to them." Then she sighed. "Sometimes I slip up."
"Like with the eyes?"
"Yeah."
Alright, this was weird. This pony (or was it a pony?) fulfilled a sleeping pony's desires? Rainbow wished very, very hard that she would join the Wonderbolts. Not-Spitfire just stared at her.
Well... maybe only those desires? Rainbow closed her eyes and brought up an image of Applejack. Wishing hard that she would be kissed by the orange mare, Rainbow waited...
And felt lips on her own. Rainbow pulled away softly and looked into the - thankfully normal - eyes of Applejack.
"So," she started, "you go around to ponies dreams and fulfill their romantic desires."
"Yes." Not-Applejack shrunk back, completely uncharacteristic of the real Applejack. "Are you going to leave now?"
Rainbow scoffed. "Why would I do that?"
The sadness that had been at the back of Rainbow's head shrunk, and Not-Applejack looked up hopefully. "You aren't?"
"No!" Rainbow grinned. "You want to fulfill fantasies, I want to have fantasies. Seems alright in my book."
The remaining sadness in the back of Rainbow's mind receded and Not-Applejack smiled. "Thank you," she whispered. Rainbow imagined that Spitfire would take her out to a nightclub to profess her true feelings...
But for the third time that night (day? dream? Rainbow's subconscious asked), lips pressed against hers. For the third time, Rainbow opened her eyes, and a third pony was before her. The pony had a pure white coat, with a flowing red-and-pink striped mane. A tapering horn grew from her forehead, and an image of two ponies kissing in front of the moon was on her flank.
"Thank you," the mare whispered, "for accepting me."
And then Rainbow was in a bed, with Spitfire pawing playfully at the sheets. The older mare leaned forwards, offering her lips to Rainbow.
"Hang on," Rainbow said, putting a hoof to Not-Spitfire's lips. "You aren't Spitfire." Not-Spitfire opened her eyes wide with shock and hurt. "You are you, and I want to get to know you better, you know? What's your name?"
The brightly-colored pegasus was replaced by the white unicorn. "My name is... well, I don't know. I guess you can call me... Shipping, I guess."
Rainbow smiled. Leaning forward, she pulled Shipping into the bed with her. The rest of the night's dreams were sweeter than any she had of Spitfire.
Arrgh... I'm tired and need to get up tomorrow morning. Damn, that actually ended up being serious. Ah well, enjoy. Or not. Not happy with the way it turned out, but you try having any interaction with abstract ideas :/ This was the best I could come up with.