Chapter Text
I wanted to establish in this story that Reader is a badass. They never sat still as a child, was always doing something. From camping, survival, martial arts, cooking, gymnastics, musical instruments they did everything. Reader was hiking on the mountain, didn't pay attention, and ended up down the hole. Meet a timid Flowey who tries to tell Reader what the deal is but is instead trying to get them to hide before “She” shows up; she being Toriel. Toriel was... okay, read: a little unhinged, very protective, and a little violent against those that look to harm “what's her's”. When they try to leave later she tries to kill them “just so I know you didn't suffer”. They get away with the help of Flowey, but now they have to trek through Snowdin with nothing.
So you have Reader trying to get through the forest undetected by the residents. They do a pretty good job getting away from the dogs having a couple of close calls maybe. They don't meet Sans until the bridge before Snowdin. Sans had been watching them from the shadows this whole time having an off feeling all day and not really expecting to see a human. So they go from having to survive in this unknown place to having to survive the skeleton brothers.
Of course it's slow going, Sans pretty much hates/is indifferent about humans and Papyrus thinks you're less than dirt and only a pawn to be used for his gain. To take down the tyrant that is the king. It was written in a way that that would have been the second time Asgore was described that way (Toriel first described him that way). Flowey joins them permanently at one point. This is where some world building/character development would happen. Reader had the brilliant idea that so long as they have a mask and are essentially cloaked (like magic hiding their soul or something) they'd be OK outside.
That could lead to them being caught and Sans is like 'great now I have to babysit you because if you get dusted I'm dust'. First they're annoyed with each other, then they have a silent truce of sorts, and then they end up at Grillby's. When you enter Grillby's there's one monster that tried to intimidate Reader and asked why they were wearing a mask seeing it as them hiding and being weak. The Reader wasn't having any of it and snarked back 'because fuck you that's why' which kind of surprised everyone. They were able to eat in semi peace. Things start to become a little friendlier between Reader and the brothers
Things progress into a scene where Reader is at the brother's home (maybe have a moment where they refer to it as just 'home' and is surprised by it) when Sans comes home injured and tries to hide it. They grab him by the hood. “Sit yo ass down before you hurt yourself more.” Then they go about patching him up. “Why are you helping me?” “You're hurt, I can help you so I am. You don't like it you can just bite me.” He grabs their hand and lightly bites them on the wrist. It makes them jump but laugh, and they smack him on the forehead pushing him back on the couch to deal with his wounds.“Do you think even the worst person can change?” Sans asks “Change? No, but that doesn't mean the offender is meant to never be happy again. You are only as happy as you let yourself be. Don't let past mistakes cloud future opportunities. Do things for you not for society.”
Feelings start to develop as Reader and Sans see that they actually somewhat enjoy each other's company. They go to Grillby's more often. Drunk Bun tries to get San's attention to hook up with him but he's more hooked on his feeling for Reader. Drunk Bun thinks that by killing Reader she'll have him all to herself. But Drunk Bun is all bark and no bite and cant stand up against Reader let alone Papyrus. It's a whole scene in the middle of Snowdin but no one is killed. Reader says to set an example and if people were smart they'd follow the person of power as they find other avenues than violence.
That act doesn't go unnoticed. The king refuses to have any point of weakness so he sends a summons for Reader. They aren't scared this is exactly what they wanted, a way to safely(mostly) get through the underground and give this “tyrant king” a piece of their mind. The kind is harsh and cold asking the meaning behind Reader's display. They try to explain that violence is not the answer and that it'll only lead to further violence. The king refuses to have any kind of weakness in his kingdom, when the barrier is broken he needs a strong unflinching army to take revenge against the humans for what they have taken.
Reader proclaimed that they weren't part of any army, hell not even part of his kingdom pulling off the mask. Why? Who knows, but they were ready when Asgore tried to impale them with his trident. They were pretty evenly matched but Reader was able to get the upper hand because of their smaller stature and flexibility. They were able to pile drive him to the ground from behind and use their weight to hold him down. He still goes on about how there's no other way and humans need to get what they deserve.
They make him stop and think. They had about a year of martial arts training and they were able to take him down. What does he think will happen if people from the military come in. They're the equivalent to the Royal Guard any they aren't afraid to show it either. Plus does he think that humans haven't evolved since he last saw the surface? Oh honey, they could wipe the monsters out without even having to step foot on the mountain and monsters wouldn't even have time to react.
They were then tasked to basically give the monsters a history lesson on humans. Though at the cost of revealing themself. They had a badass moment doing so. They were standing with the king as he explained then when they were unmasked the reaction was almost immediate. Undyne was in the crowd and hurled a spear towards them. They caught it mid air and dropped it without a reaction. Yes it burned like hell and severely damaged the hand. The lack of a reaction had the monsters frantically whispering.
They worked with the one person that was obsessed with humans and had a lot of different books (like history and science), Alphys. There were times when they were worried they'd be Alphys's next experiment, and after one trying day they called her out. It shifted to the topic of morals to which Alphys argues 'I have morals, I just choose to ignore them. How do you expect science to grow if you worry about frivolous things like that. A little immorality here could mean the difference of many living or dusting in the future'... that is a logical point.
Over time, with encouragement, monsters stopped being as violent. While they could never change how the LV has affected them they can and will do better. Slowly, but surly, they started pursuing things that their society would have deemed 'weak'. They opened up little by little and were able to mostly get back to the monsters they once were. Because of that the barrier weakened. Without the hate, malice and death of the underground to feed off of with a strong enough magic the barrier was destroyed. Now they had to work towards a peaceful coexistence.