It had been three months since she took her last prank too far.
Her friends tried to tell her, tried to warn her. Her pranks were getting out of hoof, she was going to hurt someone if she continued. She wished she had listened. But it was too late for regrets now.
It was such a simple, yet effective idea. Sabotaging cookies so she could infect the whole town at once. How could she have known that the Rainbow Juice she had used would have terrible side effects, far beyond just giving them rainbow-colored mouths? It turned them into mindless zombies, only concerned with obtaining more rainbow juice and infecting other ponies in the process.
The plague had completely engulfed the residents of Ponyville before she could stop it, and she barely made it out alive as well. By the time she could fly to Canterlot to warn the Princesses, it was spreading across Equestria at large, overwhelming the guards sent to contain it. Now, she might be the only pony left.
Rainbow spent her days staring out the window of her hiding place, watching her former friends and neighbors stumble around on the street below. She had returned to her home town in a self-imposed exile of shame, hiding in her house day after day, only leaving during the night in order to scrounge for food. Friendly faces passing through in the streets became rarer and rarer, until now, where she hasn't seen a non-infected pony in weeks. Winter from Cloudsdale was three weeks late, the red and orange leaves still up in the trees with no racing hooves to shake them down. Dash felt as if she was in purgatory, being punished for her stupid, reckless mistakes.
The blue pegasus sighed and pressed her forehead against the glass, her breath fogging up the window she stared through. Her once-proud wings were unpreened and unkempt, her brilliant mane shaggy and growing down to cover her face, her body skinny and frail from a diet of grazed grass. She didn't even know how she kept going — she barely could get out of bed in the morning, with no friends to see, no activities to do... it felt like she was just waiting for the end to come to her. To finally take her and finally end this cruel punishment of fate, of having to see the consequences of your actions every single day — the only one to survive her mistake.
However, as she rested against the window and closed her eyes, she was startled out of her thoughts by a pounding noise. She yelped in shock and fell out of her chair, becoming a tangled bundle of wings and limbs on the floor. Was that... a knock? A knock on her door. It was too light and deliberate to be somepony trying to break her door down; maybe fate really had come to take her, having decided that her punishment had gone on long enough... or maybe the zombies below had figured out how to knock, in an attempt to draw her out. There was only one way to find out.
Rainbow climbed to her hooves and carefully made her way to the door, undoing the multiple locks keeping it secure before turning the handle and pulling it open enough to peek through the crack. Standing on her porch were five ponies, none of them showing the telltale signs of infection. But they weren't exactly ponies — they had fangs poking out of their mouths, large puffy ears, and leathery wings pressed against their sides. She had only seen them once before, carrying Princess Luna's carriage on Nightmare Night. Batponies? What were they doing here?
Four of them brandished weapons and armor, on the lookout for any infected ponies, while the fifth was dressed in fancy diplomat clothes and jewelry, standing in front like he was the one who had knocked. When he noticed her open the door slightly, his eyes with slitted pupils focused in on hers with a slight smile. "May we come in?"
Rainbow blinked, glancing between the ponies standing there in front of her door with suspicious eyes. "Depends. Who are you?" Her voice was hoarse and cracked, like she hadn't used it in weeks.
"My name is Apryx, and these are my bodyguards," the well-dressed batpony said with a nod, waving his hoof to gesture to his soldiers. "I'm a diplomat from the Batpony Kingdom, in the 'Badlands', as you call them. You are Rainbow Dash, correct?"
Dash blinks again, opening the door a little bit more so Apryx can see more of her face. "...Yes. What do you want?"
"You are the last pony left in Equestria," he responded matter-of-factly. "Everypony else has been infected by the rainbow mouth scourge that has overtaken your lands. We want to help you."
"Help?" Dash asked, letting out a harsh laugh devoid of any happiness. "Why would you want to help me?"
Apryx shuffled his wings against his sides and glanced away briefly. "We had our reservations, yes... but I think it would be a mutually beneficial agreement. You see, us batponies rely on pony blood to survive, as I'm sure you already know. We cannot drink the blood of the rainbow mouth monsters, or we will become infected ourselves. If ponykind is wiped out, we will starve."
"So... what are you suggesting?" Dash asked.
"We will cure the rainbow mouth disease, Rainbow. We have figured out how on our own citizens. However, we would like to receive payment for our efforts, if we are to help you. If you let us in, we can discuss terms."
A... cure? That was beyond even her wildest daydreams. It hadn't even occurred to her that there could be a way to reverse the rainbow mouth... she had fallen so far into her depression and self-pity that she had lost all hope. Yet here was hope, back again, standing in front of her door.
After taking a few moments to regain her composure and find her voice, Rainbow nodded. "...Sure. C-Come in."
"So... how much blood do you want again?" Dash asked as she looked over the paper in front of her, containing the terms of their agreement.
"500 milliliters from each Equestrian citizen, every three months," Apryx answered, licking his lips at the thought.
"I dunno, that sounds like a lot..." Rainbow murmured, glancing around at the guards surrounding the two of them. "...Is that a lot?"
Apryx shook his head. "No, no, that is just the amount of a standard blood donation. Three months is more than enough time for your blood to be replenished."
Rainbow gulped. "It still feels like a lot... How about once a year instead?"
"If you feel uncomfortable with three months... we can extend to six months instead. One year is too infrequent, we would run out before then," Apryx conceded.
"Alright, six months is fine," Rainbow nodded, glad that she was able to haggle for at least something.
Apryx nodded and amended the contract to six months before sliding it back to the cerulean mare. "All it needs is your signature, Miss Dash."
Rainbow took the feather quill in her mouth and dipped it in the inkwell, holding it over the paper. This was it. She just needed to sign this, and everything would go back to normal... like the last few months were just a bad dream. She took a deep breath and pressed the tip to the paper, scribbling her name on the dotted line.
As soon as her quill lifted off the page, Apryx snatched the parchment away from her, rolling it up even before the ink could dry, obviously relieved she had finally signed it. "Perfect! Guards, you may get to work. Tell the others as well, please?"
The four guards nod and immediately file out of her house and into the street below. Apryx watched them leave before turning and offering his hoof to Dash. "Thank you, Rainbow Dash. You will not regret this. You may watch the process, if you so wish."
Rainbow shook his hoof with a stunned sigh, still not believing that this was really happening. "I'll... do it from here. Thank you."
"You're very welcome. I'm sure you will find that this will be a mutually-beneficial agreement. I will be in touch with you and the rest of the Elements soon."
With that, the Batpony Ambassador smiled and turned, leaving her house and closing the door behind him, leaving Rainbow alone once again. However, she wasn't alone as a broken, distraught mare with nothing to live for...she wouldn't be alone for much longer. She trotted over to the window and sat down in her chair, watching the rainbow mouth zombies stumble along below. In the sky, what looked like an army of batponies was descending down onto the derelict town, swarming down with practiced efficiency to attack every street, sealing the cookie zombies off and getting to work.
Dash watched as one of them landed in the street next to her home, letting one of the zombies move closer to him. By the pony's purple fur, purple mane, and purple eyes, Rainbow recognized her as Amethyst Star, one of Twilight's old friends. Her colors were faded and her eyes were dull and unfocused as she stumbled towards the batpony soldier, growling softly. The batpony held a white hoofkerchief in his hoof, and when the mare got close enough, he used his other hoof to keep her at arms length, pressing the tissue against her muzzle and wiping away the rainbow juices from her face. Once he did that, Amethyst went limp and flopped onto the ground, her body twitching as her color gradually returned.
Soon, she looked just how she did before she was juiced, and she sat up with a groan. "...W-What happened?..."
Rainbow blinked in disbelief. "...That's all it takes? Really?"