Sans/Toriel 30 Day OTP Challenge
Day Fourteen: Stargazing
Prompt: "Your OTP stargazing. Where are they doing this? Are they out camping? Are they sitting on a rooftop? What constellations are they looking at?"
Notes: and now for something completely - or hopefully at least somewhat - different~! We're taking a little detour back to the Underground for this one :) it's my first shot at a neutral ending, so this was interesting to write! I guess technically this isn't stargazing in the strictest sense of the word, but I kinda already wrote a UT stargazing fic (Hold Up Half the Sky - which is Alphyne not Soriel, but still there's only so much poorly wikipedia'd constellations one can take) so I didn't want it to be too similar. Hopefully you guys enjoy anyway :D
For as long as Toriel had languished in the Ruins, her first few steps outside of the door and into the rest of the Underground were some of the hardest she had ever had to take.
Because the truth was, as much as she yearned for company, after all these years there was also a perverse kind of comfort in her loneliness, a familiarity that would be lost the moment she set foot outside of that door. Toriel was no fool; she knew well what people would say about her, those that even cared to remember she existed in the first place. She was weak, selfish, a coward, she had abandoned her people just as she had betrayed her husband, when they all needed her most. None of it would bother her – for she has endured far worse than a few unflattering names - had she not harboured the suspicion, a sickness twisting in her stomach in the dead of the night, unable to escape into sleep while surrounded by reminders of all she had lost, that perhaps they were right.
Something changed, however, the day she stood in front of Frisk in yet another futile attempt to prevent another child passing through that door. Toriel recognised a gleam in the child's eyes that both excited and terrified her, as she realised simultaneously that she could never hope to stand a chance at stopping them – but also that perhaps they stood a better chance of making it on the other side than any of the others, as they weaved and dodged her wisps of fire magic while maintaining steadfast eye contact as though they knew, somehow, that Toriel could never have brought herself to hurt them. Of course, she still worried about them as soon as that door swung shut, she still replayed the moment over and over again in her mind, wondering if she could have done more, said or done something that would have convinced them to stay with her. And yet, somewhere deep in her soul, she also began to feel the first flickers of hope that perhaps, this time, their efforts would not be in vain. Perhaps that is why, upon realising Frisk had travelled all the way across the Underground to meet Asgore, she did not hesitate to leave – for despite all the trepidation she felt, if she still had a chance of saving one – just one – child from meeting the same fate as the others, she may yet begin to atone for her past failures.
And, in the end, she did – but it had not come without cost. For the same day Toriel saw the human child ascend to the surface, as she hoped but did not dare to believe they would, she saw her former husband crumble to dust before her eyes. Though perhaps she did not have the right, Toriel wept for Asgore, for whatever trace remained of the man she once loved as she saw the Underground turn to terrible disarray, the people grieving for their king and for all that he had promised, their greatest hope for freedom cruelly and unjustly snatched away, once again. That first night, Toriel simply sat there on Asgore's throne, the tears trickling down her cheeks and matting her fur no longer for the Ruins of her past, but for this New Home, as it had once been. She could no longer hide from the reality of their situation – she chose to come back from her self-imposed exile, and now she had a duty. With a final sniffle and a sigh, she rose to her feet, walked over to the throne she had fled from all those years ago and swiftly pulled off the thin sheet that covered it, coughing as the dust that had been gathering for decades filled her eyes and nose.
Toriel did not envision herself ever willingly resuming her rule – but then, hidden away in the Ruins, having warned children so many times that the Underground was a dark, dangerous place that she herself lived in fear of what was on the other side of that door, she never imagined that the Underground would need her again. And, as daunting as it is to meet the unrelenting glare of the public eye again, it also gives her a renewed sense of purpose. To have so many people – her people – looking to her for guidance, she finds herself growing more determined than ever not to let them down, that nobody – monster or human – will have to suffer as they once did. Though her new policies do meet some murmurings of dissent, Toriel is also overwhelmed – and genuinely touched – that there are so many monsters willing to welcome her back with open arms. She realised, in those last few moments before they parted, just how much of a difference Frisk has made, how many souls they have touched just by showing them mercy, by being a friend. Yes, it is eerily reminiscent of the angel in the prophecy, but Toriel can no longer afford to pin her hopes on a fairy tale. She can only try to hold onto what she felt in Frisk – the love and compassion that Toriel wishes to rule by, to preserve and nurture and extend to her people, in place of the fear and hatred that governed them all for so long.
It is not an easy transition, for any of them, but Toriel feels there is change in the air, her heart warmed by the sight of everyone pulling together. Her new school is a success, and she is as relieved as she is grateful to see Undyne – Asgore's fiercest supporter since she barely reached Toriel's knee, the most dedicated captain of the now-disbanded Royal Guard and, if Toriel is honest with herself, perhaps the monster she was the most apprehensive about meeting again – take to teaching like a...well, like a fish to water, she supposes, pouring all of her passion for bringing humanity to justice now into keeping the children of the Underground fit and healthy. Alphys, the new Royal Scientist, also seems very sweet, if needlessly flustered whenever Toriel stops by the lab to see how her research is coming along, but she promises she is working on a solution that will one day enable them to pass through the barrier peacefully, and that she too will not give up.
And, of course, there is Sans – the voice that once brightened Toriel's long, lonely days in the Ruins, now in the metaphorical flesh and literal bone. Their circumstances are very different now; his services as a sentry are no longer required, so naturally Toriel offers him any number of available administrative positions in her court, or even tending to the gardens alongside his brother, but Sans declines, telling her in that way he has where she cannot always tell whether he is joking or not that he's not sure he is ready for such a responsibility, and that he still has some ambiguously-worded "stuff to take care of".
Regardless, he still stops by the castle as often as he can, and Toriel finds herself looking forward to these visits more than ever, the joy of actually being able to open the door after their customary knock-knock joke and seeing Sans' fixed smile widen as yet undiminished. There is a thrill in leaving all of her daily worries and responsibilities behind, if only for an evening, when the door closes behind them; it is almost as if she is experiencing the Underground anew, no longer bound by fear or duty to one place, and no longer alone as they walk through the quiet tranquility of Waterfall.
"So this is where you used to work?" she asks, as they arrive in a secluded but cosy corner of the cavern, empty but for a small wooden sentry hut and what appears to be a telescope.
"One of the places, yeah – depending how you define 'work'. I think I might even still have..." Sans disappears into his former post for a moment, shuffling around under the counter where Toriel cannot see before he emerges with an orange creation in either hand. "Hot dog? Wait, don't tell me – you're more of a cat lady." Toriel smiles, glancing down at the miniature menagerie – though a little dusty, they are not without their charm. "Sorry it's not much of a royal banquet," he adds, meeting her eyes with a sheepish grin, "but, y'know, these things have been selling like – well, like hot animals lately. I sold twenty-nine just the other day."
"My, that is impressive," Toriel says, trailing a finger along the 'hot cat' as though petting it, "and, I am sure, with good reason. But I think I shall leave it for another time, as much as I do like to sample the, ah...local cuisine."
"Suit yourself." Sans shrugs amiably, before taking a bite of the dog himself. Despite the 'royal banquet' remark, Toriel is relieved that he does not seem intimidated by her royal title, for initially she could not help but worry that it would affect their friendship, that the ease and familiarity with which they addressed each other through the door – when Toriel was "Door Lady", and Sans was most often simply "my friend", although in her head she sometimes enjoyed thinking of him as her "mystery man" – would be lost if she revealed her true identity. But meeting in the flesh-and-bone has been more wonderful than anything she imagined, for there is simply no comparison between a disembodied voice behind a door that may have been inches, but could as well have been worlds away, and Sans, her friend, showing her his favourite places, laughing with her, smiling at her...
Well – perhaps, if Toriel is truly honest, it is not strictly true that nothing has changed. It is becoming harder to deny the unexpected, but not at all unpleasant spark of...something in her soul when they are laughing so hard they have to lean on one another for support, or the frisson of electricity when their hands might brush in passing – or even moments such as these, when the soft glow of Waterfall catches the light in Sans' sockets, dancing between curiosity and amusement as they meet Toriel's eyes, and she feels almost as if she has been caught doing something she should not. But to address that would present another set of complications entirely, and Toriel has no desire to do so tonight, so she simply smiles back before averting her eyes to the telescope.
"And I suppose this would be another of the tools of your trade," she comments, running a paw over the smooth plastic surface, "for spotting any passing humans, yes? May I take a look?"
"Sure – knock yourself out."
Toriel lowers her head to peer into the eyepiece, but she cannot see much of anything due to a garish red smear across the lens; she draws back, and as she blinks she feels an alarming wetness, as though something is caught on her eyelashes. "Sans, I am not sure your telescope is working..."
"It's not – oh. Uh, actually, Tori, maybe hold off on that just for a sec –" It may be the fastest she has ever seen Sans move, crossing from his post to her side with an urgency that would concern her, if he did not immediately break out into a wide grin like a mischievous child when she looks at him expectantly. "Actually, never mind, you're good. Maybe just a little red-eyed."
"What is it? Did you do something to the telescope?" Toriel demands, trying to stay stern despite his poorly concealed and inconveniently infectious amusement. She rubs her eyes and blinks down at her paws to see an unsightly red stain. "Is that...ketchup?"
"Okay, in my defence," Sans begins, no longer attempting to disguise the laughter rattling his bones as he holds up both hands in an unconvincing show of innocence, "I wasn't exactly expecting the queen to stop by anytime soon. Sorry, Tori – c'mere, let me get that for ya."
Toriel sighs, smiling despite herself as he beckons her over, but relents, bending down as gracefully as she can until they are almost nose to...well, the little hollow where nose would normally be, for she cannot claim to be familiar with the intricacies of skeleton anatomy, but up close it is curiously endearing. Toriel has a peculiar urge to nuzzle it, but manages to restrain herself as Sans gently wipes the debris from around her left eye – and then, to her astonishment, proceeds to lick it straight off his fingers.
"Still fresh."
"Oh, do not eat it!" Toriel exclaims, pushing him away and scrunching up her nose in disgust, though she is unable to stop a few giggles from escaping as she plants her hands on her hips, shaking her head in exasperation. "Goodness, Sans – whatever am I going to do with you? I am beginning to think someone ought to cook you a proper meal. Do you know..." She pauses, smile turning a little more sly as she detects an opportunity for revenge, "for a moment there, I almost believed you were about to kiss me."
She winks and the light in Sans' sockets almost disappears completely for a moment, before he lets out a pffffft of incredulous laughter; it may be the blue glow of the cavern across his cheekbones, but Toriel believes he is blushing. "Heh – wow, okay. I, uh, don't remember that being in the job description when I signed up. Come to think of it, did I even sign up?" He smirks, ducking from her gaze to run a finger around the eyepiece as though checking for leftovers; an unspoken but palpable tension lingers in the air until he continues, hastily changing the subject: "Actually, I didn't really get this to watch out for humans. I just, uh...like to look at the stars, sometimes. I mean, I know they're not the real stars, but it's...something."
Sans still sounds a little embarrassed, as though he is divulging something intensely personal; Toriel is unsure as to why, but she smiles and nods, hoping to put him at ease again. "Perfectly understandable. It is beautiful out here."
A silence settles over them as she takes in the view; inevitably, much of the Underground has changed in her absence, so it is somehow reassuring to find Waterfall just as she remembers it, unspoiled by the turmoil of the city, the light of the sparkling stones glancing off the water's edge just like the paintings of the true stars in her old history books. Despite all that she has lost, Toriel still feels fortunate to know that this place is still here for her, and that she is here with Sans.
"At the lab," he says after a moment, "Alphys has this big simulation of all the stars up on her screen. She says it's as scientifically accurate as we can make it for now – it was an ongoing thing, gathering our research, inputting the data. We used to look at it, map out the constellations...I mean, I'm not sure the guys on the surface would've actually named them 'Undyne's abs', but..." He shrugs, and they share a knowing chuckle as he catches Toriel's eyes. "It's still pretty cool to see them all. You should ask her to show you sometime."
"It sounds wonderful. Perhaps I will do just that." Toriel pauses, trying not to sound too interested as she asks: "I did not know you and Alphys were close. Snowdin and Hotland are awfully far apart, are they not?"
"Huh? Oh, yeah – well, we kind of worked together a while back, y'know, before I was a sentry. Nothing too important, just working out some...stuff." This information immediately piques her curiosity even further – she never would have taken Sans for a scientist, but evidently they still have much to learn about each other, though she cannot help wondering whether he is being vague due to the nature of their research, or perhaps even his past relationship with Alphys.
As queen, it is technically within her rights to demand he tells her everything he knows, if she believes it to be pertinent to national security – but even if that were the case, Toriel has absolutely no desire to exert her authority in such a way. Sans is – and she hopes he always will be – her friend, her equal, her...well, certainly more than simply another of her subjects to be ruled over. Besides, she reminds herself, she should not be such a nosy old woman – Sans is a big bones, in soul if not in stature, and is free to spend time with whoever he pleases.
So she settles for an equally non-committal hmm in response, and waits for him to fill the silence that follows: "Anyway, I guess that's the view from up here – you can see more down by the river."
They make their way along a short path into the adjoining cavern, bathed in an eerie blue glow from the various flora, and emerge from the silence into a chamber filled with whispers and rustles, fragments of conversations long forgotten rising from the cyan blossoms. Toriel remembers the echo flowers, of course – they are an institution of the Underground for their striking appearance as much as their unique abilities – but somehow, their hushed but persistent murmurings as they walk through the fields are a little more unsettling than she remembers, barely comprehensible snatches of words drifting by her ears before she can catch them almost mocking, almost as if – and Toriel knows this is absurd – they might be talking among themselves about her, watching, whispering, judging.
"Are you a star?"
"Hmm?" Toriel startles at the curious, childlike voice, stopping in her tracks as her head jerks instinctively to look back over her shoulder – it was so clear, so distinct from the general murmur, for a moment she is sure there must be someone else in the room with them, but of course it is just Sans, who raises a quizzical brow bone.
"I, uh, didn't say anything."
"Of course not. Sorry – it is just the flowers, I know." Toriel manages an apologetic smile, running her claws self-consciously through the fur on the back of her neck. "Do not mind me, I just...I have not passed through here in some time. I suppose I had forgotten just how...lively they can be."
"I guess they are pretty talkative today. Hey, buddy..." Sans ambles over to address one of the flowers on the side, "why so blue?" Toriel cannot help snorting at the dreadful joke as the flower repeats the question in earnest, and he continues, glancing back at her: "You know, I was actually thinking of planting some flowers myself."
"Oh, you were?" Toriel's ears prick up in interest. "How lovely! Which kind? It may be a little difficult to grow them in Snowdin, but if you need any help at all, I would be more than happy to –"
"– but then I realised...I hadn't botany."
"Oh!" Toriel bursts out laughing; Sans starts to snicker as well, which the flower to join in, followed by the one next to it, and the one next to that, until almost the entire field is laughing along, an unorthodox yet oddly striking symphony of braying giggles and deep chuckles playing out over the fields and echoing through the cavern. It is quite surreal, surrounded by the sounds of her own mirth – and, oh dear, does she always snort that loudly? – yet when she looks back at Sans, after they have both stopped laughing but nevertheless exchange wide, foolish grins, curiously comforting, as the flowers begin to feel more like old friends again. Eventually the fields quieten, the last remnants of laughter dissipating into the air, but the warmth in her soul lingers.
"Well," she remarks, grinning back at Sans, "I be-leaf you have a most appreciative audience here."
"I know, right? Maybe I'll start carrying a few of these around with me – my career could really blossom." They laugh again, too softly for the flowers to catch this time, and Sans adds: "Still not the best audience I've ever had, though. I mean, no one beats you."
Toriel beams, feeling her cheeks flushing unexpectedly at the compliment and hoping it is not too visible in their darkening surroundings. "Why, thank you. I am pleased to hear I am not so easily replaced in your affections by echo flowers."
"No way. Well, unless they somehow develop the ability to make pie – then maybe you got some competition, Tori."
Toriel chooses not to dignify that with a response, scoffing and shaking her head fondly at him as they approach an area she recognises: the grassy bank right next to the river, always a favoured picnic spot. They have no food now, although it would not surprise her if Sans were to produce yet another variety of hot animal from his pocket – sometimes she is sure he must be carrying half the Underground in there – but he simply sits, bones cracking as he stretches his legs out, and after a moment's hesitation Toriel joins him, gathering her robes to arrange herself as comfortably as possible. The grass is a little damp, but she does not mind.
"Y'see, that's the other thing about these guys," Sans says, nodding towards the flowers flanking them on either side of the river, "they seem so harmless. You say something, they say it back, it's all good fun. I mean, they're flowers – of all the dangerous things down here, you'd never think they could hurt anyone, right? But once they're done kidding around, people forget they're here, and they forget how much they hear. And some things – well, maybe some things weren't meant to be heard, and some things you don't wanna remember. But, here, they don't forget, not until they've passed on whatever they've heard. And they get to hear...a lot."
There is barely any change in Sans' usual monotone, but he does not meet Toriel's eyes as he speaks, his skull turned up towards the sparkling stones overhead; for a brief instant, a cloud of darkness seems to pass over his face, as though he is seeing – or remembering – something up there that she cannot. Then it is gone, as he glances back at her and cracks a smile, but his sockets do not brighten as they usually do when it is genuine. "Heh – sorry. I guess I kinda spaced out for a moment there."
Toriel smiles at the pun, but she hopes he will continue; she has rarely seen Sans like this, quiet and contemplative, and while a part of her is concerned about what he could have seen, to say such things, she cannot help but find it fascinating, too. "Not at all. You are quite right – I suppose we all have things we would sooner forget, which we would not want passing freely among the flowers."
"Right." The corners of Sans' mouth appear to lift a little higher as he looks back at her, before speaking again. "So, me and Papyrus used to come here all the time as kids, right? Not a whole lot else to do around Snowdin, but we always had a blast. Then, this one time...we were around here, chilling by the river. Paps was practicing his attacks, and I – well, I guess I fell asleep. But next thing I know, he's shaking me awake, terrified, absolutely crying his sockets out, saying he wants to go home, we have to go home right now."
"Oh, no!" Toriel presses a hand to her mouth at the thought of anything happening to dear, sweet Papyrus. "What was the matter? Did something happen to him?"
"He was crying too hard to tell me, so obviously I had to get us out of there as fast as I could. We get home, I manage to calm him down, and eventually he tells me a flower said something mean to him. Then all the other flowers started saying it, too, and he tried to run away but they were everywhere, they just kept saying it...He thought it was his fault, he'd done something wrong, because they were all being nice to him yesterday."
"Ah, I see. Oh, the poor dear." Toriel bites her lip, the image tugging at her soul. "Did you tell him –"
"I tried to explain that they weren't actually talking to him, they're just flowers, they just repeated whatever they'd heard – but I don't think he got it, or if he did it didn't seem to make him feel any better. So that night, after Pap's bedtime story, I came back here when no one was around. I went to all the flowers – every last one of 'em I could find – and I told them...'The Great Papyrus is the most sensational skeleton in Snowdin!'. 'No – in the Underground!'. 'The Great Papyrus always produces the most perplexing puzzles!' 'The Great Papyrus is gonna be the strongest, toughest, coolest Royal Guard ever!' Stuff like that – well, I didn't want them to sound like me," he adds in his normal tone by way of explanation, chuckling a little too as Toriel stifles a giggle at the endearingly unconvincing falsetto. "Anyway, the next day, I got up early – okay, Tori, you don't have to look that surprised – and Papyrus really didn't want to go back to Waterfall, as you can probably imagine, but I promised him it'd be worth it, the flowers had something very important they wanted to tell him, but we had to go soon, before anyone else got there. So we did, and, well..." Sans shrugs, but Toriel already sees the genuine pride and affection shining through in his smile at the memory, "judging by the look on his face when we got there, I'd say he got the message."
"Ahhh, how wonderful. I am so glad that story had a happy ending." Toriel feels her own smile tugging at the corners of her lips, as it inevitably does whenever Sans talks about Papyrus; even from behind the door, she could always hear the smile in his voice, the fierce, unconditional love behind every word, even when he was complaining that he'd moved his sock collection again. Back then, as much as it warmed her soul, she could not help but feel a pang of something like envy listening to those tales, reminding her of the family she no longer had. But now, it fills her with a new kind of hope, now she has seen for herself the love that still exists in the Underground. She wants – no, she has to protect that love, watch it blossom and thrive, in all its forms, for the sake of all of her people as much as for herself. With that thought, she reaches out and gently places her hand on top of Sans' where they rests on the grass between them. "That was a very sweet thing of you to do for your brother."
"Oh...heh, no, it was nothing really." He grins back at her a little sheepishly, shrugging shrugging off the compliment like he does most things; she has noticed that Sans often seems slightly uncomfortable with, or perhaps simply unaccustomed to praise. Still, Toriel does not intend to stop giving it where deserved, and he does not move his hand away. "I mean, I had to do something. No one messes with my little bro – especially not some dumb flower, right?"
"They certainly do not – unless, of course, they wish to have a bad time," Toriel agrees, and they exchange wry smiles, recent events coming to mind. Perhaps flowers are not the most trustworthy sorts, after all. "Well – as I said, it was long ago, but we also used to bring the children here. Asriel loved to see the stones, the echo flowers – he took it all very seriously indeed." She smiles, warm and wistful; she can still hear him clear as day in her mind: "Mooom, don't watch! I can see you peeking! It has to be a secret, remember?". "I did not like them running off into the fields alone," she explains, "so, whenever wished, Asriel always insisted that I turned around, covered my ears and closed my eyes. Because if I heard his wish, it would not come true, you see?"
How many years had passed, since they were all here; some days it seemed only yesterday, when Toriel and Asgore would sit here, snuggled up together and looking fondly on as the children played. Chara never seemed too interested in the echo flowers, but they liked to sit and swing their legs in the river, deliberately splashing Asriel to make him squeal. And now...now there is only Toriel, a familiar, yet no less sharp twinge of guilt and sorrow in her soul as she gazes up at the sparkling stones, wondering how many wishes had been made here, and how many had ever come true. Was it fair, for her to be the one who survived? For all the times she had failed her family and her people, could Toriel truly say that she deserved her place, her title? If she could have given her own life to change any of it, she would have, in the beat of a soul – but what good would wishing do now, when...
"Hey." Sans interrupts her reverie, and she sees his sockets soften at the edges as he shuffles a little closer, gently bumping the top of her arm with his shoulder, a brief but comforting touch, "if you never found out what they wished for, it could still come true, right?" Toriel smiles and nods, grateful for his unspoken understanding that no more needs to be said, that now is not the time to discussing such matters. "Then I guess maybe we should make a wish. Since we're here."
"I suppose we ought to honour the tradition." Toriel closes her eyes, out of habit more than anything; she has naturally wished for many things inside of this room and out of this room, though with diminishing hopes over the years that any of them would come true. But now, she wishes that Frisk, wherever they may be, is safe, and happy, and loved. She wishes for peace, for the strength to help the Underground find its way again – for all his faults, she realises, Asgore had held onto that hope, even if it ended up destroying him, for the sake of his people – her people. She wishes to preserve that hope for them, and for herself, wherever she may find it – perhaps even in moments just like this one, when she opens her eyes to the gently amused twinkle in Sans' sockets, and smiles sheepishly back as she wonders how long he has been looking at her.
"That looked like some intense wishing there. I thought for a sec you'd fallen asleep and I was gonna have to carry you back to the castle."
Toriel lets out an undignified snort of laughter, pressing a hand to her muzzle at that rather sweet yet hilariously improbable image. "You would carry me? Oh, Sans – as generous as it is of you to offer, I'm afraid I must question whether you have the backbone for such a task."
"Are you calling me spineless?"
"Come, now – do not skullk with me." Finally recovering from their mutual fits of laughter, she manages to ask: "Did you make a wish, too?"
"Might've done," Sans replies, elusive again, but this time shooting her a wink so as to leave no doubt as to the answer. "I can't tell you, Tori – else it won't come true, remember?"
"I would never ask you to. I was simply curious if you had considered wishing for a new telescope," she smirks, unable to resist teasing, "as you seem to be having some trouble keeping that one clean."
"Brutal, Tori. You really goat me there." Sans winces, making her giggle as he clutches dramatically at his shirt, as though mortally wounded. "That's okay, though – the sweet thing is, you can see most of the constellations right here. See that up there?" He points up to the ceiling, Toriel's eyes following to the biggest, brightest stone illuminating the river. "We call that one the Tem Star. Or, to give it its full title, uh...Temmius Ijustmadethatupicus."
They continue in a similar vein, tracing out imaginary images in the sparkling stones – a hot dog here, a snail over there, a smiling face before they start to become increasingly specific and nonsensical, making up ridiculous "facts" to make each other laugh. The distance between them seems to grow increasingly smaller, leaning in closer together for warmth – or perhaps simply because they want to, and Toriel cannot help but be grateful that they are a safe distance away for the echo flowers to pick them up. Not because they are saying anything that ought not to be repeated; but simply because, after a lifetime of the entire Underground knowing all her personal affairs, there are some moments – like the way Sans' head falls back against her shoulder when he yawns in the middle of telling her all about the long and complex history of the River Person's Belt, and remains there until they depart – that Toriel would like to keep for herself.
Perhaps the stars above them are not the genuine article, but looking up at their sparkle, all of the hope and promise of wishes made and those yet to be fulfilled that bounces off of the river, shining down on them, Toriel cannot imagine anything brighter – or more beautiful.