Author's Note

You've made it to the second chapter, good job! I must warn you, there's a little squicky stuff in this one such as peeing and the mention of diapers. If you've got the patience, read on and the good stuff will be coming soon!

Chapter the Second

The cave felt even colder, the cold biting through Celestia’s sopping wet coat, mane, and tail. She shivered and groaned softly. A long unfamiliar voice echoed through the cave. She stepped over to the wall that kept the Fountain a secret for so long, confirming her fears in the reflection. I’m… I’m a young filly… She looked over herself; she couldn’t have been taller than a foot and five inches. Her mane and tail were a bright pink and no longer flowed like her older self. She looked like a normal filly. Luckily, she still found her cutiemark.

She shuddered, closing her eyes. I have to get back to Canterlot. Her horn lit up and sparked as she again attempted to teleportation through the crystal wall. Depsite all her might and concentration, she couldn’t pull it off. Her body must have been weakened by the change. Young fillies don’t have the physical means of controlling their magic, after all. She whimpered instinctively before catching herself. No, I’m stronger than this… I just have to contact Luna. She can get me out of here. Once again, she gathered all her strength and reached out telepathically to her sister.

“Lun-...-an you-...-me?”

Luna flinched at the sudden voice in her head. She was in the middle of her Night Court when she heard the familiar voice of her sister. Something was unusual about this time, the usual strength and clarity of her sister’s voice not shining through. She knew something had gone wrong. Her sister never had trouble communicating with her before, even in the deeps of the crystal caves.

“Night Court adjourned! We have important matters to attend to!” Luna was already out of her seat before the guards and ponies lined in front of her throne could process this declaration. They looked at each other, confused and worried by the Princess’s sudden change in demeanor. Luna walked quickly through the main door and out towards the castle gates. She spoke to the guards at the front. “If We are not back within the hour, send a search party down to the crystal caves. That is all.” The guards looked at each other and then back to Luna, nodding in agreement.

Luna traced Celestia’s arrival to the cave, growing more worried with every passing minute. She rushed through the long-memorized twists and turns of the caves and soon arrived at the sapphire wall she feared her sister had been trapped behind. With a quick teleportation spell, she was on the other side, looking around frantically for her sister. Luna gasped as she saw Celestia’s horseshoe on the ground, soon finding the pile of her royal raiments.

“Sister! Sister, where are you?!” Luna shouted.

“Not so loud, dear sister. I’m… I’m down here.” Celestia responded.

“Down… here?” Luna asked, a bit puzzled by her sister’s choice of words. Then she looked down. Luna put a hoof to her mouth as she saw the now much younger version of her sister. “W-What happened?”

“I slipped an’ fell into the Fountain.” Celestia put her own hoof to her mouth, eyes wide. She realized that a slight lisp had come with her new body.

Luna hid her smile well, not wanting to upset Celestia. “Well, we should get back to the castle. Perhaps something in the royal library can help us find a solution to this… predicament.”

Celestia tilted her head and offered a rebuttal. “While I would be glad to do so, how would we esplain this to the guards?”

Luna tapped her chin with a hoof. That was quite a problem. They couldn’t just tell the guards that there is a Fountain of Youth under Canterlot. Then an idea struck. “Magical backfire. Every unicorn knows that holding back a spell for too long can have any number of detrimental side effects. This one just happened to be age regression.” Luna smiled as she spoke her thoughts.

Celestia thought about this reasoning for a moment. It sounded believable at the least, and really, it would be their only way to keep the secret of the Fountain secure. “Very well. That is our escuse.” She nodded in agreement.

Luna used her magic to levitate Celestia onto her back, nodding in affirmation. “Then it is agreed. Now, let us return to the castle.” Luna hummed. She teleported the two of them through the wall again and made her way back out to the dark night of Canterlot. Luna flew them both back to the castle, presenting their explanation to the guards without any questioning.

As Luna was carrying Celestia to the royal library, she noticed a warm sensation dripping down her back. Startled, she stopped in her tracks. Celestia tilted her head, looking confused.

“Why did we stop?” Celestia asked.

“S-sister… we think you are urinating on us.” Luna stammered.

Celestia’s face flushed a bright red as she looked down to see herself trickling pee onto her sister. She shot her forehooves down and pressed them against her crotch, but the flow had already stopped. “I-I-I…” She stuttered.

Luna took Celestia off her back and shuddered. “Your body must be regressed more than we thought.” Celestia hid her eyes behind her forelegs, utterly embarrassed that she had an accident on her sister. Luna gently pushed Celestia’s legs out of the way and looked into her eyes. “It is no consequence, sister. Do not be ashamed. We should have foreseen your young body being unable to handle such stress without consequences. Do not worry.” Luna said, trying to comfort her sister with an unusually soft voice.

Celestia seemed to take offense with Luna’s tone. “H-hey, I’m not actually a filly. I still have my mind.” She huffed.

Luna shrugged. “Really? I would not know that considering how you are acting.” She retorted.

With a sigh, Celestia relaxed. “You’re right; I need to pull myself together. I’m sorry, sister.” She apologized.

Luna smiled. “It is alright, sister. However… we do fear this complication will happen again. Would you mind if we took some precautions?” Luna questioned.

Celestia arched a brow. “What sort of precautions?”

Luna sighed slightly, knowing that her sister would not be happy with her suggestion. “I think we should put you in protection.” Luna stated.

Celestia nods. “That sounds alright. We wouldn’t want anypony to harm me while I am in this state.” She added.

Luna looked away from her sister. “I-I meant a different kind of protection… Diapers.”