"So wait, your name is actually Luna, not Woona?" Asgore asked in surprise.
The few monsters that had not immediately raced back into the Underground to gather the necessities of living on the surface now sat in the main dining hall of Canterlot Castle, where it sat jutting out the side of the mountain that, all unwitting, had long been the prison for the Monster race. Asgore, Toriel, Undyne, Sans, and Asriel sat alongside Celestia and Luna as they told stories of Luna's time in the Underground, and in turn heard stories of the surface. Princess Temmie vibrated around the table, nibbling whatever caught her interest and flopping on her back to wave her paws in the air in frustration whenever this wound up being something inedible.
Celestia chuckled as Luna nodded her head firmly. "The nickname 'Woona' came from difficulty she had pronouncing her own name when she was younger," Celestia explained readily, holding Luna close under her wing, plainly overjoyed to have her little sister back after so long. "Though even when she was able to pronounce it properly, she frequently exaggerated her former lisp because it made her more adorable, which helped her get her way with the castle staff."
"Is that why you did it, Luna?" Asriel asked curiously. "Went by Woona underground, I mean? For 'cute armor'?"
"Nuh uh!" Luna insisted. "I called myself Woona because Mama did!"
"But I called you Woona because you introduced yourself as Woona," Toriel explained. "And why didn't you correct me later?"
"When you spelled it Woona in the runes, I thought it was a phonetic difference!" Luna complained, blowing a raspberry at Celestia when she chuckled at that.
Celestia chuckled softly at the interchange, but marveled inside at how much Luna had accomplished so young. She was very proud of her little sister, of course, but it put an uncomfortable onus on herself. If Luna could accomplish so much by her fifth birthday, how much more could reasonably be expected of Celestia herself at 12?
As she thought about this, Sans spoke up. "there's one thing i'm wondering, though," he offered calmly. Celestia did her best not to shiver, as the smiling skeleton still uneased her with the way his voice seemed as much in her head as in her ears. "the human kids who fell down, they all had ample reason of their own to climb to the top of the mountain where no one returns from. why'd luna go? with how much you love each other, i can't imagine why she'd want to run away from that..."
Celestia visibly winced at the question. After all, she knew beyond a shadow of a doubt that Luna had run because of what she'd done. She'd had no right to behave that way towards Luna. She couldn't have known... "We...got into a fight," Celestia explained. "I...yelled at her, put unfair blame on her for things...things I should not have blamed her for..."
"We both yelled, Tia," Luna whimpered, nuzzling her. "S'not your fault..."
"But...why did you go up?" Celestia asked, sorrow and confusion mixed in her voice. "You know the peak of the mountain is forbidden..."
"Uh huh," Luna confirmed. "That's why I went, and took what I would've taken if I was running down. Knew you'd look down first, so I'd have plenty of time to pout. But everything was so different..."
"you got curious, walked up to the edge of the hole, and tripped?" Sans offered. When Luna nodded, he chuckled. "so rather than any desire to disappear, simple curiosity led you to the biggest secret of all."
"When we couldn't find you for so long, I was so scared..." Celestia whimpered softly.
"I didn't mean to fall or get lost!" Luna offered, half complaint half consolation. "If I'd known that, I'd have at least packed a sandwich!" When this resulted in laughter all around the table, she pouted. "What? Tia makes the best peanut butter sandwiches, and she always leaves a couple for me in the cold box in case I need a snack!" Much to Luna's consternation, this resulted in even more laughter. Sighing, she waited until the laughter died down, then nuzzled Celestia. "Sorry I broke the cookie jar..."
Celestia winced slightly, but nuzzled back. "It's alright..." she offered consolingly. "It is a small thing. You shouldn't let it sit so heavily on you..."
"Well," Toriel spoke up, "perhaps some cookies might make everyone feel better?" Reaching into a pouch, she pulled out a plate of cookies. "Made to my own recipe, like my pies."
"Ooh!" Luna squealed happily, eagerly reaching for the cookies. "Tia, Mama makes the best cookies!"
"Yes..." Celestia responded absently as she picked up one of the cookies. She politely took a bite...then froze, staring down at the simple morsel as the mix of cinnamon and butterscotch gently caressed her tongue, melting in her mouth in such a startlingly familiar way. Without warning, she dropped the cookie and burst into tears.
"Tia?" Luna asked worriedly, nudging her. "Tia, what's wrong?"
"Is something wrong with the cookies?" Toriel asked worriedly. "Did I do something-"
Before anyone could say anymore, Asgore stood up. Gently lifting Celestia into his arms, he carried her out of the room and to one of the side corridors. The others started to follow, but Sans quickly hand signed them to remain. "don't worry," he offered softly. "this is something i think the king's uniquely suited to help with. i'll go keep a quiet eye on them." And with that, he vanished into a shortcut, the fall of the barrier and distance from the void seeming to strengthen such abilities rather than weaken them, as it didn't even leave behind a hole in space-time - however brief - as it once had.
Asgore watched over Celestia carefully, waiting until she'd cried herself out and achieved at least some self control. He felt both pride and sorrow when he saw how quickly she brought herself under control, recognizing the skills of one trained to rule, but having been learned far too soon. "I'm terribly sorry," Celestia offered with practiced grace even as she wiped her eyes and muzzle with a handkerchief Asgore offered her. "I don't know what came over me-"
"I do," Asgore interrupted softly, his voice full of empathy and compassion. "It was the same recipe your mother made, wasn't it? The very same recipe that the last of which was in that jar Luna broke?"
Celestia stared up at him in stunned amazement, then finally nodded, unable to say or do anymore.
Asgore's gentle smile was encouraging and comforting as he sat against a pillar, settling the pony - so tiny, and yet already so responsible - in his lap. "How long ago did they pass?" he asked gently.
Celestia managed just barely to clear her throat. "J...just over two years ago..."
"Then it was on the second anniversary of their death that you discovered the jar had been broken," Asgore deduced softly. "And the last treats your mother had made for you both shattered and lost, despite every effort you'd put to preserve them however long you could, to in some way keep her with you both?" He felt his heart shrivel as he saw the stricken look on her face, knowing just how clearly he'd seen through her. "Child, you are not the first to make a mistake in the heat of grief and anger, and in doing so drive the one you hold most dear away from you...nor will you be the last. Be grateful that both you and Luna are so young, that such a mistake can be easily corrected, and the wedge between yourself and Luna so easily removed. In a matter of months or less, it will be forgotten, and you and she will be closer than ever." He sank into his own thoughts briefly. The division between myself and Tori...that will take far longer to repair, if ever it can be...
Celestia sighed wistfully. "I...I only wish it could be so," she admitted sadly. "But...the duties of the throne, they are many...and only increased with an entire new tribe amongst us. As Princess, I have to shoulder all I can, and give Luna as much time to be a child as I may..."
Asgore shook his head in amazement. "Dear child, why is one such as you forced to take so much upon you? Why have you no Regent to aid you?"
Celestia shook her head slowly. "I...I don't really understand the reasons for myself, but I can't..."
"Perhaps I can explain it, Highness?" a unicorn mare in a homespun cloak offered, having rounded the corner as the discussion reached this point.
"Would you please, Miss Clover?" Celestia asked hopefully. "I...still don't get it..."
Clover nodded with a soft smile, then turned to Asgore. "Our nation is not as united as it might look to an outsider," she explained. "We are three tribes, visibly distinct from each other, and until recently were three nations that cooperated uneasily before coming to the brink of war. It was only the appearance of beasts of powerful magic that fed on the energies of our distrust and division - driven back as we discovered the power of our unity - that we realized we had to act as one people to survive. However, even now the frictions remain, and the danger of open conflict remains. For no one tribe will accept a ruler who is of one of the other two tribes. When Celestia and Luna were discovered - two alicorn children, with aspects of all three tribes - we saw the way to unite ourselves. Their parents could act as their Regents while they lived, because none would believe a parent would deliberately use their children for power, or allow their children to be used. But with their passing..."
"No such Regent is left available," Asgore concluded. "And Celestia, to protect her sister, has sacrificed her own childhood to grow up far too soon." As Clover nodded, Asgore stroked his beard in thought. "Clover, I think I might have an idea to help...but I will need all perspectives on this matter. Do you perhaps know two others - one each of the other two tribes - who could be trusted to seek the best for all regardless of tribe, and unafraid of reprisal for such considerations?"
Clover smiled warmly. "I know just the ponies," she responded firmly. "They just happen to be my two closest friends, actually...and have the ears of their tribal leaders, as I do."
"Couldn't be better," Asgore murmured softly. "Gather them, and Toriel and I will meet with you all, so we can find a way both to ensure peace between Monsters and Ponies, and to ensure the safety and happiness of even the littlest of us." He gently stroked Celestia's mane as he spoke, offering her the comfort he knew she needed so desperately.