#winter toriel

[zelphin124]

SeasonTale - Chapter 5

TW: Abuse Oh boy... the plot thickens. Some could argue, this is where the real story starts. Winter POV, let's go.

Masterpost

~o0o~

The horror in their eyes struck his heart. 

He had the targets pinned against an alleyway wall. They cowered in fear under his knives. Their eyes were shaking, and the younger monster started to cry. 

Winter glanced down at the two creatures whose lives were in his hands. Despite his younger age, they still were at his mercy. 

It wasn’t supposed to be this way. 

W!Gaster’s voice rang in his ears. They are traitors, they had to die, they deserved to die… 

But why? 

None of it made any sense. They didn’t do anything wrong… they just disagreed with W!Gaster, nothing more. Why did they have to pay with their lives for having an opinion? 

Winter felt the tears that escaped his eyes freeze on his face as the harsh wind beat against his skull. He lowered his knives and stepped away from the two monsters. “Go,” he squeaked. “Go before he kills you himself.” 

The two monsters thanked him and bolted away. 

He heaved a great sigh. What a relief. It brought him peace to spare the lives of the innocent. He hadn’t done that before… but he knew from how he felt that it was the right thing to do. 

That peace quickly faded when he realized what punishment he would receive for committing such an act. Would W!Gaster throw him out to fend for himself in the storm again? Would he hurt him?

Would his father kill him? 

Winter didn’t want to think about it. He broke the crystalized tears off his face as he felt the books in his cloak get heavier. He shoved down his emotions and refused to feel them. There was always a looming reminder that his emotions were a weakness anyway. 

Stepping out of the alleyway, Winter!Sans removed the cloak from his face and walked quietly into town. He hoped that he could time his visit to the librarian just right that his father wouldn’t expect anything. 

Twenty minutes…

* * *

“I’m glad you enjoyed the books, Winter.” Winter!Toriel placed the books on the shelf before turning towards the child. “I’m even more grateful that you could read them.” 

Winter nodded silently as he sat in a chair away from the windows. The library was warm and extensive. There was a small desk that he sat in front of next to the hallway that revealed thousands of books on massive shelves. Winter wished to read all the books within the library but felt he couldn’t. An impending doom of getting caught grew heavier each time he came. Winter believed W!Gaster was catching onto his distant behavior, and he didn’t know how to mask it well enough. 

“Would you like some new books? I had a new collection come in…” Winter!Toriel paused, glancing back over at Winter!Sans. She tilted her head in concern as she observed him twirling his thumbs and staring at the floor. “Are you okay?” She asked gently, approaching him and leaning in front of him. 

Winter desperately tried to hold back his tears. “I couldn’t-” he gasped. “I couldn’t kill them this time…” 

“Oh, honey…” W!Toriel extended her arms and wrapped them around Winter. “That’s nothing to be upset about; you did the right thing.” 

Her embrace was so foreign to him. What is she doing? Was she going to attack him from behind? Why was she not moving? Winter didn’t know how to react. In fact, he just cried… the tears ran down his skull as he tugged on her cape. He didn’t want her to let go… her embrace was comforting, something he had never felt. 

“You are very touch-deprived, dear.” To Winter’s dismay, she let go and looked him in the eyes. “You feel better about not hurting them, right?” “Yes, ma’am,” Winter nodded. 

“That’s good, that’s how you should feel,” The librarian nodded slowly before standing up. She sighed with great worry before looking at Winter once more. “Winter, It’s… It’s not good for you or anyone else to stay with your father… I… I believe you need to leave.” 

Winter glanced up at her, his tears drying up. What did she mean? Why would he leave his father? He couldn’t go out in the snow again and expected him to return to the mansion promptly. “But I need to go home in ten minutes, or he’ll be mad.” 

“Honey, you wouldn’t return to him, ever,” W!Toriel explained. “You would run and start a new life, free from him and his evil plans.” 

… I can be free? 

The librarian kneeled in front of Winter, her voice hushed. “Listen to me closely, Winter. I can help you,” she glanced at the door before continuing. “The rebellion against the gasters wish to save you. They would help raise you in a much better environment than you are now.” 

Winter didn’t understand much of what she was saying. However, he knew what the rebellion was. It was the highest form of treason against the gasters to be a part of it. Winter gave slow and painful deaths to those accused of it and watched others suffer in W!Gaster’s grasp. The fact W!Toriel was even mentioning it means that Winter would have to kill her. 

Winter drew his knives, causing Winter!Toriel to back up. “I… I have to kill you. The rebellion is what my dad has ordered me against.” 

“But they can free you,” She insisted. “They will give you a much better life than you have now.” 

Winter’s hands were shaking with the knife in them. Everything in him told him not to attack the librarian, especially after all she’d done for him. However, he was told the rebellion was dangerous, and orders were orders. “The rebellion is bad-” 

“Is that what they call us now, the bad guys?” 

Winter and W!Toriel stared at the monster standing in front of the hallway. The boy’s jaw dropped. It’s the goat from the photo in my room… 

She looked similar to Toriel; the same species. However, she was much shorter and her horns were curved. Instead of wearing a blue gown patted with snow, her clothing was pure starlight and shined white like the snow on the ground. Her gaze penetrated with an uneasy amount of determination and power, but there was also understanding and care. It was a look Winter never understood. 

“Put the knife down young boy,” the starry goat demanded. “It is not your destiny.” 

“W-Who are you?” Winter’s voice quivered as he obeyed, laying the knife on the floor. Although he recgonized them from the painting, and had a good idea of who she was, he wasn’t sure. 

“I am Season!Toriel, co-leader of the rebellion against the gasters and the rightful queen of SeasonTale.” Season held her head high, looking down at the boy. “And I am here to rescue you.” 

“Well, I was going to introduce you to her, but it looks like introductions have already been made,” Winter!Toriel scratched her head, chuckling nervously. “I said you could live a better and happier life, Winter. If you go with Season, she will ensure of that.” 

Winter’s entire body was shaking now. There she was, the former ruler of SeasonTale, standing right before him—the ultimate target of W!Gaster, and the main threat to his throne. Winter had only read about her rule and power. Although she was a good and caring leader, his unfortunate circumstances have ruled him against her. He was only a boy, and he feared his death would come upon him any moment now. 

Season oversaw Winter, her eyes softening. With eloquent grace, she knelt on the ground to make herself smaller. She extended her hands towards Winter. “You don’t have to follow your father's footsteps,” she whispered. “You can rise above that and become a good and caring leader one day. Let me help you. Let me rescue you from Winter!Gaster.” 

Winter stared at her paws before looking at Season and then at Winter!Toriel. She nodded in agreement. Winter fought back tears. He wanted freedom; he wanted to escape. This was his opportunity. This might be his only chance. 

“I can’t.” 

* * *

Each step back to the castle got more painful. His teeth gritted against one another. He had given up his only chance to escape. 

He couldn’t even figure out why himself. Was it because he wanted his dad to be proud of him? Maybe there was some hope in turning his father around… Maybe, just maybe, he could find another way. 

But he couldn’t join the rebellion. 

There was no way… After all that he had done? Sure, they are fighting for justice; they are the good guys. Winter knew they would have treated him better. 

But would they have? 

Winter had killed so many rebellion members. His entire life, despite it not being that long, he fought against them. He was a threat to them… a target. 

He was a bad guy. 

He didn’t want to be, but he didn’t see how he could change. Although there was a slim hope he held out for his father, that same hope wasn’t measured to himself. 

And it swallowed him whole. 

“You’re two minutes and three seconds late,” W!Gaster’s voice boomed as he closed a pocket watch in his hands. 

Winter sighed, closing the door behind him, and took his coat off. It took him a bit to stomp off all the snow before answering. “I apologize. I had a bit of a delay with the bodies.” 

“Right, because you didn’t kill them.” 

It was as if the boy had been shot. He froze in place, fear taking control of his mind. Panic swirled within him. How did he know? How did he find out? Was he watching the whole time? 

W!Gaster let out a low, rumbling laugh. “Did you think I wouldn’t find out? Those traitors were spotted crossing the Summer Kingdom this evening. Thankfully, I had them taken care of-” he whipped around, his hand raised. “UNLIKE YOUR PATHETIC FAILURE TO DO THE JOB!” 

Winter collided with the ground from the punch that rolled across his skull. His vision immediately blacked out. No, no, no, no… 

He didn’t see the remaining hits that were laid upon him. “You had ONE JOB! ONE HELL OF A JOB! You failed, as always! You worthless piece of-”

The rest of the insults were muffled as his hearing rang. He curled up in a ball as he embraced hit after hit. His breath was shaking, and it was almost impossible not to cry. 

He had enough. 

Winter could make out the sound of a gaster blaster charging up. He braced for impact, but when it fired, he felt nothing. 

The beating had stopped. 

Winter sat up, his vision still blurred. He couldn’t make much out except for the new hole in the wall and W!Gaster’s boots hanging from it. When he turned around, he saw that the blaster was his own. 

His eyes widened with fear. What have I done? 

The next few seconds were the most rash seconds of his life. Winter didn’t waste any time before he grabbed a different coat and bolted out the door. He couldn’t stay… he was going to die if he did. His little feet carried him to the edge of the hill. He quickly looked around for something to get him down, as the stairs were too slow. 

He heard W!Gaster’s enraged roar from the mansion. With no time to think, Winter grabbed a giant icicle from the cliff and slid down the hill on it. Although it was slippery, and he fell off it at the end, it gave him the head start that he needed before teleporting into the town. 

His heart was beating faster than he ever thought it would. His feet were aching, but that didn’t stop him as he burst through the library door, his vision blurred once more. 

Winter!Toriel glanced up in surprise before rushing over to him. “Oh my gosh, what happened to you?” 

“Help,” Winter grasped onto her arms. “He’s after me. I have to go.” 

Before W!Toriel could call for her, Season was already by her side. She glanced at his face before kneeling, offering her hand quickly. 

He didn’t hesitate to accept her offer this time, squeezing her hand as the fear of his father gripped him like a python. “Please, help me.” 

She smiled softly. “I will. Let’s go.”

[ikurko]

[zelphin124]

Here we are! Toriel Designs! Im so impressed with your skills and you did a beautiful job!

Seasontale Toriel designs for @zelphin124! It was an absolute delight to draw so many variations of goat mom! Seasontale belongs to Zelphin.

[niidsch]

UNDERTALE / DELTARUNE NEWSLETTER: Holiday 2024

[shimmershy]

Holiday sweaters!

[junebugdunes]

I miss the sun

[vinegar-chipzz]

Undertale Newsletter….

[selkiemoonssss]

Winter alarm clock redraw!

It was a super quick doodle, but I really wanted to do it because 1. I've been kinda sick the alst few days and haven't really made anything 2. I miss drawing them Anyway I really love them

[wiredratz]

Mm yummy !

[missholoska]

like father like daughter ❄️

[martlet-my-beloved]

Martlet comic my beloved. Consider Martlet bundles up Frisk like in the recent deltarune newsletter to leave the ruins. snowdin is cold plus it acts as a disguise! its a perfect plan! (until they get to any other biome in the underground)

oh the way i HOWLED when i first saw frisk's winter outfit i swear

First - Previous - Next - Masterpost

[premamelody]

[ask-undernext]

Everyone needs a warm hug this winter💗

Pls reblog if you like it

[zelphin124]

SeasonTale - Chapter 7

TW: Slavery, sickness, abuse I'm not sure how much of this I'll continue. I don't think it'll be as good as my other writing, but I do hope to get all the lore out to you guys sometime. This is not me rejoining the UnderTale fandom. Masterpost

~o0o~

Papyrus was barely alive. 

Undye took it upon herself to protect his dying soul from dusting. The time that passed that week was all a blur to Spring, and his anger that he once felt quickly sunk into a deep despair as he could do nothing about the situation. 

The managers beat them ruthlessly, using their whips and fists to double their workload. The fire from the unhealthy habits of the factory only worsened the air quality. Each day, someone got sick, and they were beat for it. 

It didn’t make any sense to Spring!Sans. Why would they hurt someone for being sick? As far as he could tell, he couldn’t control when he felt unwell. 

Which was all the time, now. 

Spring held a small piece of bread in his hands as he stared at Spring!Papyrus, laying on a bed as his skull was half-dusted. Spring!Alphys held his soul together for hours. Spring thought he heard her and Undye conversing about the workload, with Undye doing twice as much so Alphys could keep Papyrus alive. 

His brother wasn’t breathing. He sat there, his bone slowly reforming and dusting as his chest barely moved. His soul didn’t beat, either. The white heart was clasped in another monster’s hands. Had Alphys let go, he would be nothing but a pile of dust. 

Spring glanced at the bread in his hands before he rested it in one of Papyrus’ hands. “You need it more than me,” he sighed, tears streaming down his face. “Please be okay, brother…” 

There was no reply. Spring!Alphys glanced at him with worry. “Kid, you need to eat that.” 

“I’m not hungry.” 

“That wasn’t a suggestion,” Sp!Alphys insisted. “Eat it.” 

There was another whip crack outside the room. Spring shook his head and gently crawled out of the space, trying not to be spotted by the whippers as he returned to his post, fiddling with the wires. 

Cries of pain and hopelessness echoed through the air, but they were often broken by the crack of whips. They were more prominent than usual, as if their work hours were not enough, they increased them, allowing little time for rest and food. More and more of the workers got sick. Spring had attended to most of them; Papyrus had taught him a thing or two about keeping people healthy, and no one was in these conditions. 

Slavery never allowed for such luxuries as health. 

Spring couldn’t help the tears that fell down his face as he thought of his brother. They fell onto the wires, quenching their sparks. It’s my fault... I’m the reason he’s almost dead... 

He listened closely to Spring!Temmie and Spring!Mettaton’s conversation. They talked about how the ‘big boss’ was coming today. They became hushed about the topic when Spring drew closer to listen in more. The only thing he caught was the big boss being a Gaster of sorts. 

Could it be the same one who sold him for a piece of bread? 

Perhaps the pressure of said inspection is what caused the whippers to be more hostile and picky with the work that was being done by their slaves. It was almost unreasonable and insane to expect better work in worse conditions, but there was no consideration of such a fact. 

Spring gently taped the wires together on the outside of another machine as he coughed the smoke out of his lungs. His hands and feet were hurting again. He was covered in black tar and ash. It burned his skin worse than the flames themselves. There was no time to clean up, however. He had spent his free time checking up on his brother, and he had to face said consequences.

This can’t be all there is... Spring wiped his face, feeling his stomach getting nauseous. He knew he was about to hurl. He stepped away from the wires and walked over to the edge of the platforms, resting his head over the edge as he vomited into the fire. For a solid minute, his stomach desperately tried to search for any nutrients, and when it found none, it shot the acid out of his mouth. 

Spring’s cries of pain were disturbing. He could hear some of his fellow slaves approaching him, but they were pushed aside as the familiar, horrifying steps of a whipper came along. “Get back to work, kid!” The monster grabbed Spring by the scruff and lifted him up, turning him to face him. “What the hell do you think you’re doing?!”

Spring covered his mouth, trying to withhold another puke. No, please, not now—he couldn’t. His body gagged, and his vomit covered the whipper’s face as Spring coughed, tears streaming down his eyes. He looked at the whipper in horror as the goo ran down his face. What have I done? “I’m sorry, I’m sorry I—” 

“You imbecile!” The whipper threw Spring onto the hard pavement, scraping his face. He hurriedly tried to wipe the acid off his face in disgust, cracking his whip. “How dare you defile me?!” 

The whip cracked against Spring’s skull. He cried out in pain as he curled up on the floor, trying to block the whips. Instead of his face, the whips struck his hand, ripping the bones apart as the whipper continued. Blood poured out from them, and Spring whimpered, unable to put his pain into words or a cry for help. 

The whippings suddenly stopped as a loud thud could be heard. Spring hesitantly looked up through the water building up in his skull. 

Spring!Muffet had just punched the whipper in the face. 

She looked at her hands as if she couldn’t believe what she had just done, but that didn’t stop her words from snapping at the abuser. “Pick on someone your own size!” She dared to say. “You’re pathetic for picking on a helpless child! Be a man and choose someone stronger than he!” 

Spring’s eyes widened in fear as he reached out to her. “Muffet, no—” 

The whipper clearly did not find her challenge amusing. He stood up, grunting as rage fumed in his eyes. He cracked his whip to the side. “Own size, eh? Someone like you, then? You know what happens to challengers like you, right?” 

Spring!Muffet’s eyes widened as she raised her hands into fists, all six of them. “To fight for a kid’s life, yes.” 

The whipper raised his whip. It was as if time had gone in slow motion as he slowly brought it down on the monster that saved Spring—

BOOM!

A bright flash of light filled the air. There was a strong gust of wind, sending the whipper flying into the lava below, screaming all the way down. Muffet was also blasted back, barely catching onto one of the railings. Spring was pushed into the wire system, grunting as he tried to stand up, but his hands hurt too much. 

Before him, in the direction that caused a blast, was a bright, white fire. It burned the wood nearby as if it were the sun itself. Who walked out of the fire was someone Spring had never seen. It was too difficult to see, but she looked like Toriel, a similar, shorter type of goat. Her gaze was flat, and she walked with grace. Everything about her glowed like starlight, something Spring had only heard about until now. 

The shouts of the whippers were blurred. They yelled about the hole in the factory before charging at the intruder. “It’s her!” one of the muffled shouts rang through Spring’s ears. “Kill her!” 

One by one, the goat slayed every person that dared to come her way. Despite being hit with some of the whips, they disintegrated on touch. Her hands were surrounded by a white fire, and when she fired at the whippers, they turned into ash immediately. Dozens of them swarmed her, but they were no match for her skills. 

Behind her came a large dragon. It was white, with long eyes, and its head shaped like a gaster blaster. It munched on any whipper or opposer that approached the goat. It was as if it was made from starlight itself. Its gaze turned toward everyone else, turning around to reveal someone on his back. 

Spring’s eyes widened as he observed the little skeleton on the back of the dragon. He… He looks like me. 

The battle waged on, but it was something Spring was in too much pain to notice. He glanced up one more time to find the slaves cheering at some proclamation the white goat gave. She gently approached Spring as everyone rushed out of the factory. 

“Little one,” her voice was more soothing than a thousand ice packs. “Come with me; let me nourish you back to health.” 

Spring weakly looked up at her, his body trembling in pain. He couldn’t form words as the white fire that burned the factory blinded his sight. He reached out his hand, trembling. “B-Brother…” 

“Spring!Papyrus, will be alright. Come with me; you are being rescued and set free.” 

Spring felt her hands wrap around him as she hoisted him up over her shoulder. He didn’t resist as he watched more whippers being reduced to ash. Something about the sight eased his mind, as if they were getting what they deserved. 

The goat climbed up onto the large dragon, saddling it as if she rode it. She held Spring in front next to the other little guy. “Hold on,” she commanded before taking the reigns and flying off. 

Spring watched as the factory went out of sight, getting smaller and smaller as the dragon ascended into the sky he had never seen. His eyes widened in wonder, resting on the beauty of the world before him. The sun greeted him willingly, and suddenly, his soul felt lighter and more at ease. 

Spring had felt hope. 

His hands trembled as he held onto a lower part of the reigns. It took a moment for him to process what was happening, but the cool air felt so good against his skin, he never wanted to leave it. He turned his gaze to the other small skeleton in front of him. The little guy had bruises and thin, snowflake eyes. He was staring right back at Spring the entire time the dragon flew off into the air under the cover of the clouds. He nodded slowly. “Greetings.” 

Spring stared back at him in awe, as if he were looking at himself in a mirror, but a different version of him. Everything was so new, he didn’t know how to process anything that was going on. 

But that didn’t stop him from being polite. His hand trembled as he lifted it in greeting. 

“H-Hello…”

[undertalebabbleblog]

Why do Monsters in Undertale and Deltarune use Words like 'Hell' and 'God' in their Everyday Language?

Additionally, a Theory on the Time Period During Which Monsters were Trapped Underground

OKAY SO hi Pup here with more UTDR insanity on a topic that I do not have the historical knowledge to be properly qualified to talk about, but am going to talk about anyway because it's been lingering in my head for a long time.

The monsters in Undertale and Deltarune use terms like 'hell', 'god', 'damn', etc., implying that they have enough of a concept of hell, god, damnation, etc. ingrained into their society for it to be used in casual speech. But that stuff comes from human religions. It fits easily into our understanding of language, given that those are the terms we commonly use, but monsters don't follow human religions as far as we see, and the widespread use of those terms comes from the influence that Abrahamic religions have had on our society. We don't see any established monster religions at all in Undertale, and in Deltarune there's obviously the Angel.

The Doylist reason for monsters using those terms despite the lack of human Abrahamic religions in their society is obviously just that Toby Fox is a human living in our world who is used to using those terms and likely didn't think twice about including them in his game. However, that reason is not nearly as fun as going insane over minor details in video games. Thus, this lengthy post.

In Deltarune, the religion we see in Hometown is the one that worships the Angel. We don't know how prevalent this religion is in the wider world, nor how many people in Hometown actually worship it, but it's a commonplace enough belief that the town has a church in it that seems to have been around for a decent amount of time.

While it's highly possible that the worlds of Undertale and Deltarune are entirely different from ours, I am going to be operating on the assumption that they both take place in worlds that are pretty much the same as ours, with only minor differences aside from the existence of monsters, which I'd say counts as a pretty major difference.

Now, as the Angel religion doesn't have a concept of sin, we can assume that there's no concept of punishment for sin either, and therefore no hell. However, through Alvin's wording of "our religion", combined with Asriel confessing to his 'sins' despite the lack of sin or confession in said religion, we can infer that there are indeed other religions in the world of Deltarune, and at least one relatively prevalent other religion contains the concepts of sin and confession. (Susie and Lancer both actually directly mention Christmas at one point, which means that Christianity exists in Deltarune, alongside the religions and practices that are the origins of many Christmas traditions.)

Assuming that monsters were never trapped underground in Deltarune, they were likely living alongside humans that whole time, and it's therefore quite likely that they would have picked up popular phrases that reference human religions. In fact, it's likely that monsters themselves followed the beliefs of Christianity, Catholicism, or the like at some point, given those religions' prevalence. (It's also possible that this influence is part of why monsters in Deltarune don't seem to use magic like their counterparts in Undertale do, given Christianity's whole thing about magic and stuff.) Monsters, like humans, probably don't all follow the same religion (Monster Teen, for example, wears a necklace with a cross pendant. While this choice could simply be aesthetic, it's equally likely that they're Christian, Catholic, etc.). And, given the whole Angel thing, it's possible that Hometown's predominant religion is an offshoot of a pre-existing Abrahamic religion.

In Deltarune, it is not at all out of the question and in fact makes complete sense for monsters to be referencing things like god or hell.

In Undertale, monsters have been stuck underground for an unknown but very long period of time, to the point where most of the adult population has never even seen the surface. (I am NOT going to be theorising about how monsters age, because I have already been down that rabbit hole multiple times and have nothing to show for it except confusion.)

My current theory is that they were trapped sometime during the 11th, 12th, or 13th centuries, most likely the 12th. If we look at the architecture of the Ruins, the first place that was settled by monsters:

It's quite similar to Romanesque architecture, which lasted from the 10th century to the 13th and was predominant in the 11th and 12th centuries.

This style is mostly reflected in New Home

Except for in the Last Corridor

Where the pointed arches are reminiscent of Gothic architecture, which was active from the late 12th to 16th centuries.

While we know that monsters receive human garbage via the dump in Waterfall, I'm going to assume that nobody would be throwing out schematics for their Gothic windows. Therefore, considering the timeframes of both these architectural movements, monsters were likely trapped underground in either the late 12th or the 13th century, with my money being on the late 12th given the prevalence of Romanesque architecture as opposed to the much rarer cases of Gothic architecture that we see (acknowledging, of course, that we do not see all of the Underground, and that I am only working off the knowledge I have here).

More potential proof for this time periods comes from the intro, where we see the silhouettes of several humans.

There are no guns or other firearms shown, meaning that the War of Humans and Monsters occurred in a time when spears and swords were used in wars instead of guns. While I couldn't find a spearhead that matched the one depicted, there is a human shown holding a sword, which we get to see at two angles.

I originally assumed from the first image that it was a leaf-shaped blade, but looking at both the first and second images, I theorise that this is depicting a knightly sword, also known as an arming sword, used as a one-handed sword, usually alongside a shield, in the high middle ages (1000 - 1300 CE).

While still used in the late middle ages (1300 - 1500 CE), longswords were more common as a primary weapon, and arming swords were often employed as a sidearm in addition to a primary weapon. While the sword depicted in the image is too short to be a longsword, it seems to match the length of an arming sword fairly well, and we can see that its wielder is using it as a one-handed weapon, rather than the longsword's intended two-handed grip.

Now, I'd say it's likely that most or all monsters only lived around one area, since it would have been a bit difficult for the humans to trap every single living monster underground if they'd been spread all over the world. If monsters only existed around one area in the high middle ages, they could have been fought against in the war and trapped underground much more plausibly, and they could have been easily dismissed as myth in later millennia.

The prevalent religion during the Middle Ages was Christianity, and we know that there were some pretty strong opinions about things like magic and other belief systems. It's stated in the game that the war started because humans were scared of the monsters' power to absorb human SOULs, and while that was probably part of it, it's not hard to see how the humans of that time could have turned on the monsters out of fear of their magic, or even just not being human, in addition to the stated provocation of monsters being able to absorb human SOULs. We also have to remember that we only get information about what happened from the monsters' perspectives, written on stone plaques, thousands of years after the fact. We don't have the full story here, and I suspect that the conflict was already brewing, and that the monsters' recorded reason for the war was simply the thing that tipped it over the edge.

Anyway, if monsters were living amongst or near humans during the Middle Ages, they were probably following or at least had a lot of exposure to the prevalent religion and its effects on commonly-used language. (It's also possible that the symbol of the Delta Rune and the prophecy about the Angel who has seen the surface is a remnant of the Angel belief system we see in Deltarune.) Their use of language could have evolved in a similar way to ours over the centuries, words like 'hell' and 'god' becoming more detached from their religious connotations when used in everyday expressions, and, with the added influence of human media that began falling into the garbage dump in Waterfall, their use of those words, as well as language in general, became remarkably similar to our own, despite them having been trapped underground for all that time.

And... yeah. That's it. That's the theory. If someone who actually knows about this sort of stuff happens to come across this post, please feel free to add your expertise. I'm going off internet research here, I'm not qualified to be talking about this.

[rainy-matcha]

Undertale gives STRONG winter vibes