It all started with the kid. They fell, with the same determination as the first. Never hurt a SOUL, and made friends with every single monster that they met. A red SOUL, fit to be the final one, the one to break the barrier. It seemed to him that the kid would perish at the hands of their king, and that they would be free.
They didn't kill the king, Sans had saw that much, but the king had died. He perished, and the monstrous flower, as well as the six human SOULS, had vanished.
Frisk had escaped. Undyne went into a fit of rage, not believing a word of what Sans had told her. She had become friends with the human child, and they had even helped her confess to Alphys. The lizard-like monster had tried vehemently to calm her girlfriend down, but to no avail.
She brought forth revolution once the Queen had been reinstated, knowing of her plans to make sure monsters didn't harm any humans. The revolution was backed by many monsters, furiated at the loss of progress on their freedom. Monsters who had wanted to see the sun before they turned to dust. There was a large disagreement between Alphys and Undyne, and they split up before Undyne was officially unstated as the new queen of the underground.
A lot of controversy surrounded Alphys and Toriel, and the monsters of the new monarchy were making their lives harder to live than they already were. The monsters who once followed their queens every order, who admired the royal scientist for her efforts, chased them back into the ruins, where anything could come out, but only a few things were allowed in.
They welcomed the smaller confinesof the ruins, as they felt safer there than in the rest of the underground. They lived there together, Alphys repairing and upgrading technology, as well as moving her stuff in, and Toriel teaching g the Scientist to cook something other than instant noodles and peanut butter sandwiches.
Undyne paid someone a hefty sum of gold to patch Mettaton up, and reactivate his human hunting mechanics. He sought after Papyrus soon after, and begged him to be his Second-In-Command. It wasn't the position Papyrus had originally wanted, as Mettaton had been given the duties of the Head of the Royal Guard, but Second-In-Command was up there. He hastily agreed to Mettaton's request, without knowing a single thing that he would have to do.
Papyrus had went to train in the Capitol for over a month. Sans had expected his brother to ditch the job once he found out he would have to kill humans, but Paps came back a hardened warrior, trained to fight, defend, and kill. His new armor already had some dents in it, and was made of a sturdier material than his battle body. He still sported his bright red-orange scarf, but he now bore the new delta rune. Seven human SOULS replaced the prophesized angel, and there were more, smaller triangles at the bottom. The SOULS of seven humans will get them out of here. Sans warned Papyrus, and he just responded with a nod and a hug. If not for himself, or for the rest of the monsters, then for his brother, who longed to see the endless night sky and the cosmos. Papyrus knew Sans wanted to live a happy life on the surface, and wanted him to live a happy life there as well, and he now knew what it took to finally achieve that dream. Papyrus was willing to take the necessary steps to get out of this hellhole, and to free his kind from the increasingly smaller walls of the mountain they were trapped under. He bode his brother farewell, and left with very few belongings. He didn't even take his flag.
Sans had been left all alone, his family torn apart by the whims of an eight year old, and his race torn apart by kindness versus malice. Sans had grown comfortable with his life that included the human child, and had taken it for granted. He had known that Frisk had wanted to go home, but didn't know the exact repercussions of letting them leave. He had Grillby, sure, but he could only take so much of the flame elemental, and the familiar patrons of the bar and grill. He quickly became secluded.
A while later, a human fell. Alphys had discovered him, and patched him up. He had been told of the human through the large door, and had been told that he would not likely make it to Snowdin in one piece. He lacked the will to live, and with his dim, Grey soul, he would probably finish himself within the next week. Toriel and Alphys had tried so hard to keep him healthy and happy, but a few days later, Alphys brought a Grey soul in a jar to him. She had been crying when she told him that he had hung himself on the tree in Toriel's front yard. Tori had been horrified when she saw it, and Alphys had buried the body, and bottled the soul. There was no note, but he had a small smile on his face. He took the soul to Doggo, who had saddened at the story, and agreed to take the soul to Undyne. The apathetic boy had gutted what he wanted, and Sans hoped that he was at peace.
The next was a girl, in her teens. She had walked out of the ruins, no damage done to her, no escort. She had sought Sans out, asking for him by name. She was very bold and brash, her maroon soul shining like a beacon. By the time she had left for waterfall, he had thought of her as family. Their souls resonated like his and Papyrus's. She had tried to make a romantic move, and when Sans explained his feelings for her, she ran off. She ran straight to Undyne, looking for any way to leave safely. She died fighting the queen herself, and Sans couldn't help but blame himself. The trait he had known her for, her passion, had gotten her rejected, and ultimately, killed.
Sans had moped for a while, not eating, not sleeping, and going out into the snow for hours on end. He had been curled up on the couch, when Papyrus had came in. He was welcomed warmly by his brother, but he brought bad news. The next human that Sans came across was to be brought to either himself, Mettaton, or Undyne, alive, or dead. The next soul that they caught Sans guarding would get him locked in the dungeon, and he didn't want that for his brother. He hugged his shorter, sadder brother tightly, then reluctantly left the household.
The twins fell, barely five. Pretty much toddlers, Toriel had handed them to him directly. They had been getting stir crazy, and Toriel simply didn't have the room or the time to take care of them. He took care of them for a long time. Two years had passed, and everything was nice until the curious seven year olds wandered out into the forest while Sans was sleeping. He woke up to furious pounding on his door, and loud cries of 'DAD!' coming from outside. He sprinted to answer the door, and the Dog Sentries looked at him, fondly but sadly. They cuffed him and took him, as well as the twins, to the castle. He had to watch the two kids he had come to think of as his own be killed by his brother, and the underground's only idol. He was sentenced to five years in the dungeon, for protecting the snow white, innocent souls of kids he was raising. He had no regrets.
They released him as they were bringing the Fifth and Sixth souls in. Two brave, orange souls of a couple who refused to let go of each other, even though they knew they were going to die. One soul was red with determination, and the other, yellow, for the justice he wanted to bring to these child killers. He was knocked out when he tried to fight his restraints, to try and save the two youths. He wokeup in his house, with his brother shooting him an angry glance, as he walked out the door. Over the quick course of ten years, they had already obtained six of the seven needed souls to break the barrier. They only needed one more, and then they would be free to leave this cursed place they called home. The Royal Guard was rapidly expanding, with even Monster Kid joining, though only because his mother forced him to. Napstablook had fused with a robot body, much like his cousin, Mettaton, and stayed in the ruins. He hadn't talked to his famous family member since he became head of the Royal Guard. Sans had lost hope at peace, and at any semblance of family ever since he was released from the dungeon. But then came the seventh and final soul. The compassionate, pink soul of a young woman, flaring with life. She came through the ruins with the sad ghostbot, and a smile on her face. They walked through the forest, hand in hand, and he knew his life was about to be changed.
But for the better, or the worse?