They made camp near the cave and rested for the night, in hopes of building up strength for whatever lay ahead. While the rest set up the tents and other supplies, Applejack came over to Apple Bloom, who was sitting on a log that had fallen long ago.
"Y'all ok?" she asked.
She thought for a few moments. The reality was that she wasn't okay, physically and mentally, but something told her that venting her problems now wouldn't be constructive. "I'm fine," she replied, voice wavering.
"You sure? I can...go get you some water, or, some food...or somethin'? I know you must be goin' through so much right now, and I just wanna do the best I can do t' make things easier for you."
A smile grew on her face. Nothing in Equestria could keep her sister from caring too much, whether it was big or small, or in this case, completely out of anyone's control. "Sure," Apple Bloom replied. "I'll have some of that water, please."
Applejack left immediately, trotting away to fetch her request. She watched her move so effortlessly, jealous but appreciative of her willingness to provide her services to someone who needed them. As the light slowly faded, they retired to their tents, of which they'd only packed two: one for the adults, and one for the fillies. Apple Bloom wasn't sure which one to pick, standing outside in the cold for a few moments until Scootaloo called her over.
"Come on, Apple Bloom!" she yelled from inside the tent. "It's getting cold out here!"
She smiled, and made her way over to their tent. It was nice to feel appreciated, she thought to herself. That was something she'd never really given thought to before.
They arose early in the morning the next day, but the sunlight didn't last long. Instead of being out in the warm sun all day long, they immediately entered into the cold, dark cave. The light gradually diminished behind them as they ventured into the depths of the cave, until at certain depth, the pinpoint of white from the entrance could no longer be seen. As the cave became darker, the air became cold and damp, with water condensing onto the cave walls and dripping from stalactites amidst constellations of strange, luminescent creatures that dotted the ceiling above them.
Rarity eyed the drips woefully, worried they would fall onto her mane. "Are we sure this is going to lead somewhere?" She said while maneuvering around an area where droplets were falling.
"Yep," said the elder Apple Bloom, still leading the way through the caves. Already, she appeared to be getting used to her fragile body, as if things had always felt that way.
Twilight lit her horn with a purple glow to illuminate the path forward. "Are we at least past the area where you saw the creature?"
"I don't know," replied Apple Bloom. She was having enough trouble keeping her hooves on steady ground, let alone observing the cave around her.
Scootaloo and Sweetie Belle had no answer either. It had been too easy to lose their bearing in such a dimly lit cave while being threatened by a frightening creature.
Applejack eyed her sister warily, worrying she would misstep and twist an ankle. It's amazing, she thought to herself. It don't matter whether my sis is young or old. I still feel like I've gotta protect her. She watched as Apple Bloom pressed onward in the cave, toward the creature that did this to her, amazed at her bravery. As they ventured further and further into the dark abyss of the cave, Applejack began to wonder if she was who actually needed support.
Scootaloo walked alongside Rainbow Dash, occasionally glancing at her broken wing. It was wrapped tightly against her body with the bandage continuing around her waist. In a weird sort of way, Rainbow Dash breaking her wing made Scootaloo feel closer to her; like they shared a common issue. But when that thought arose in her mind, she almost felt disgusted with herself. Not being able to fly was her burden, and certainly not something she would ever want any other pegasus to live with. Even if it did make her feel closer to them.
Rainbow Dash seemed to notice Scootaloo's periodic glances. "Everything alright there, Scoot?"
"I'm fine," she replied, letting out a small laugh. "I mean, you're the one with a broken wing."
She felt guilty after saying that.
"Hey, if you're alright, I'm alright," Dash replied, wrapping her good wing around her as they walked together.
Caught off guard, Scootaloo felt a wave of wholesomeness fill her spirits that made her smile. It had been awhile since they'd interacted that way, and it was always a surprise she welcomed and relished when they did. She walked closer to her adopted big sister, feeling content in the moment.
Suddenly, Twilight's horn stopped glowing, and they were immediately enveloped in darkness.
"Twilight!" exclaimed Rarity. "What are you doing? I can't see anything!"
Confused, Twilight tried to relight her horn, but it was to no avail. Her voice was all that penetrated through the absolute darkness. "Something's wrong. I can't use my magic!"
Rarity held in the urge to scream. "Everything is fine," she said to calm herself down. "We're just in a cold, wet cave. It's stuffy, and dank, and we can't see a thing...surrounded by who knows what..."
"There must be some sort of magic cancelling out my spells," said Twilight, frustrated and still trying to relight her horn.
"Hold on, everypony," said Applejack, calmly. "I've got just the thing -- an old-fashioned, reliable light source."
She rummaged through her saddlebag, while Twilight gave her a look of annoyance, and felt around for the lantern she'd packed, then pulled it out. It took a fair amount of time to find the matches, but eventually she lit the lantern and illuminated the cave around them.
"Oh, thank Celestia," said Rarity.
"Thank me," replied Applejack, her voice muffled as she held the lantern in her mouth.
As they continued to walk forward, the cave gradually opened up and the air became warmer. The sounds of dripping water seemed to cease as well, and the floors had become more smooth and polished. After rounding a corner, the cave in front of them expanded outward considerably in all directions.
"Whoa..." said Sweetie Belle and Scootaloo, awestruck.
The light from Applejack's lantern bounced off chiseled walls, illuminating the large room considerably well. In front of them was a large, vertical barrier with ornate depictions surrounding its perimeter. Pictures of creatures with swirling horns, majestic wings, and long tails had been chiseled along its border. In the center at floor level was a small opening, and high above them toward the ceiling was a larger opening with a small platform extending out from it.
A young but authoritative voice reverberated off the walls from the opening above. "Who presents themselves at the entrance to The Highlands?"
Apple Bloom stepped forward carefully, squinting upward toward where the voice was coming from. "We were brought here to fix a problem."
"There is no problem here," the voice responded. "Our only problem was solved long ago. In any sense, you are not permitted to enter."
Applejack spoke up. "Who ain't permitted, exactly?"
"You aren't," the voice replied promptly. "Only the young ones behind you are permitted to enter, should they pass the test of youth."
"What about Apple Bloom?" asked Sweetie Belle.
"The elder? She is the least qualified to enter."
Rage began to build up in Applejack's eyes. "She was transformed that way just hours ago by one of you!"
The air was silent for a few seconds. The voice returned, with a hint of curiosity. "What say you about her being transformed?"
Apple Bloom decided enough was enough. "A Niril did this to me."
The voice paused again. "A Niril, you say? And where did this Niril go?"
"Here," she replied.
"...I see."
Small hoofsteps echoed off the walls as the creature high above them presumably left without saying another word.
"...Now what?" said Scootaloo.
Moments later, a bright blue creature flew out from the opening near the ceiling, spreading its wings as it descended toward them gently. It fell gracefully, like a feather, and they stepped backward as it landed in front of them.
"I am a Lirin," said the creature. All in all, it was barely larger than Sweetie Belle or Scootaloo, but with its wings unfurled it seemed much larger. It was just like the depictions had shone, but even more grandiose with its vibrant blue fur contrasting the surrounding rock and stone. "And I am sorry for what happened."
"Can you undo it?" asked Twilight, beyond excited to be discovering an entirely new type of creature and to learn about its magic.
"Yes I can," it replied.
They waited.
"Well?" said Applejack. "Can't you do it now?"
The creature sighed. "Have the ways of our kind been this lost to the outside world? Apparently so, judging by your lack of basic Lirin knowledge. I can transform your elder to their original state, but only at a cost. When a Lirin performs an age transformation, it must draw that energy from somewhere. Every interaction must have balance. Otherwise, things descend into chaos. So if I transform her, I must either transform myself or draw the energy from something else. And I do not so willingly give up my youth force to strangers whom I have hardly met."
Applejack stepped forward. "Then draw that energy from me," she replied. After seeing her younger sister transformed, she'd never felt more sure of something before in her life.
"Applejack," said Twilight. "Are you sure?"
"I'm sure," she replied.
"I'm afraid that won't be enough," said the creature, somewhat surprised at her willingness to give herself up so freely. "I simply cannot risk drawing so much energy that the source is drained completely."
Sweetie Belle had been silent for quite a while, lost in contemplation. After having their altercation with the Niril and feeling an odd connection with them, she felt a sense of bravery overcome her.
"Then use me too," she replied.
"Sweetie Belle!" exclaimed Rarity. "But you're so young! What if you become...older than me? Your big sister? Let me take your place."
Scootaloo walked forward. "Use me instead." She looked back toward Rainbow Dash, knowing that's what she would have done.
Rainbow Dash nodded in response, holding back the pride welling in her eyes.
The Lirin creature seemed genuinely amazed. "That would be more than enough. With two young sources, I will have no need for the older mares who volunteered."
Scootaloo and Sweetie Belle walked forward and stood next to Apple Bloom, in front of the Lirin. It began to kneel before them, but Apple Bloom spoke. "Wait. How much will this change them? And me?"
"The young ones will only become slightly older and mature. The spectrum of life is not equal. The side of old holds little life, and the side of young is overflowing with it. The middle has some, but it pales in comparison to the life of youth. As for you, elder one, it will bring you to around the same age as your friends. All three of you will never be who you were before, but it will be close."
The air was silent for a few moments. Apple Bloom considered refusing their offer, but knew deep down they would never let her. "Continue."
The Lirin resumed kneeling before them, its swirling horn of blue pointed toward their center. It leaned to the left and touched Sweetie Belle with its horn, and fog of wispy tendrils began to come from out of her and into the creature's horn. It then leaned to the right toward Scootaloo and did the same. They both slumped toward the floor slightly, all too familiar with the feeling from the creature that had did the same to them before, but it only left them feeling slightly tired and woozy this time.
The Lirin was now holding the aura within its horn, glowing a bright blue. It seemed to pause for a moment, as if considering something and wavering between what it wanted to do. But it quickly dismissed its thoughts, and knelt its horn toward Apple Bloom. The wispy tendrils emanated out from its horn and into Apple Bloom's forehead. As it did so, the Lirin stood taller, and ever-so-gradually, returned to its hooves as Apple Bloom transformed before their eyes. Her wrinkles smoothed, her joints softened, and her eyes became wider and more vibrant as her entire body shrunk downward, her perspective returning to normal.
The creature breathed a sigh as the last remaining wisp of life swirled into Apple Bloom's body, revealing a somewhat older mare than she'd been before beginning this journey. The same was true for Scootaloo and Sweetie Belle.
"It is finished," said the Lirin.
"...Thank you," said Apple Bloom, surprised at how easily the words formed in her mouth. "Can we thank you somehow?"
"No thanks is necessary," it replied, "I transformed you because the creature that aged you is not welcome in our land, and I believe you may be necessary in finding it so we can banish it again."
"The Niril?" replied Apple Bloom.
"Yes, of course, the Niril." The creature seemed somewhat annoyed.
"But didn't y'all live together in peace and harmony, or somethin'?" asked Applejack.
"For a time, yes. But those times are gone and the newer times have proven to be better."
Applejack eyed the Lirin suspiciously, but didn't proceed any further.
"Well, can we at least know your name?" asked Sweetie Belle.
"Yes. My name is Sigil, and if you three could please follow me into this passage, I would greatly appreciate it."
"Can't we bring our sisters?" asked Scootaloo, her eyes locking with Rainbow Dash. "She has a broken wing, and--"
"The rules are clear," said Sigil, "I cannot permit any creature that cannot withstand the tests of youth, and I can tell by looking that they cannot."
Apple Bloom rose her voice. "But--"
"It's okay, sis," said Applejack. "We all knew this would happen eventually. Y'all just be careful, okay? We'll be waitin' right here for your return."
Something about Applejack had changed, Apple Bloom realized. But her thoughts were interrupted as Sigil wrapped its wing around them to guide them into the narrow opening at the barrier's center. They entered one by one, with Sweetie Belle entering last.
"Bye," she said with the purest voice they'd ever heard.
As she turned around and went into the entrance, Rarity's eyes welled up with tears and she returned her response.
"Bye."