Chapter Text
When the human fell down, Sans was 11. He'd grown up learning in school that humans were dangerous. Far more dangerous than he could know. One morning, he, Papyrus, and their mom were out. Sans was excited, it was rare Auntie Mel babysat, but when she did Sans loved it. Especially because Mel was in New Home. There was another person in New Home Sans adored, Grillby. Grillby had been friends with Sans forever and was also babysat by Mel. Arial paused midway through Waterfall. There was a human covered in dust, wearing glasses and carrying a dusty notebook. Arial stepped in front of her sons, "Boys, I need you to go to Mel's by yourselves today."
Papyrus let out a whine, "But mom, you always take us."
Arial turned around, a stern look on her face, "You know the way to River's boat. Head back and get on, that's an order."
Sans froze, "Mom, what's happening?"
Papyrus tugged Sans's wrist, "C'mon, Sans, mom's mad enough already. Let's go."
As the two boys walked, Sans heard the sound of a battle starting. He pulled Papyrus behind a large rock and the two watched. Arial had a wide stance to keep herself balanced, sword drawn, "Human, you appear to have killed a monster. That I can't allow."
The human had a desperate look, "No, please I didn't mean to, I didn't mean it I swear!"
Arial pointed the tip of her sword at them, "As the captain of the royal guard, I cannot allow you to harm another monster."
The human backed away, flinching as their back hit one of the stone walls blocking any escape, "Please, please it was in self defense! I was attacked first! I was hit first! I didn't mean to kill them, please!"
Arial scoffed, "I don't trust human scum. Not after what your kind has done."
Somewhere deep in the back of his mind, Papyrus had always known this was what his mom did, that didn't mean he wasn't horrified anyway, "mom…"
Sans tugged Papyrus back behind the rock as one of the human's attacks missed, "Be careful!"
Papyrus looked at Sans, "We have to get out of here."
Sans peeked out again, "What about mom and the human?"
Papyrus shook his head, "Leave them. She's a royal guard, Sans…this is her job."
Sans solemnly nodded, taking Papyrus's hand, "Alright."
Arial glanced back, freezing as she noticed Sans and Papyrus hadn't left yet, "Boys get out of here!" She turned back, gasping as one of the human's attacks hit her.
They looked terrified, "I'm sorry ma'am!" They tried to run, but she dragged them back into a battle.
She gripped her sword tighter, "Right, now you've made me angry, human."
Sans turned back as both the human and Arial landed attacks on each other at the same time. He broke away from Papyrus, "Mom!"
Papyrus ran after his twin, "Sans don't!"
Arial panted, falling to one knee, "Damn it, you're strong kid. But unfortunately for you, I'm the captain of the royal guard for a reason."
Sans rushed to Arial, "Mom!"
Arial turned and gasped, "Sans." The human launched an attack in his direction, seeing a chance to distract her and get away. Arial dove to get in front of him, despite knowing her HP couldn't take much more. Sans was weak, his HP was low, even for a growing monster. Time seemed to slow. She could see Sans's terrified face, him stumbling back in horror. She knew her HP had dropped before she even felt the blow. All at once it sped up again. She coughed, staring at the ground.
Sans fell to his knees, "Mom! Momma, I'm so sorry." The human ran off, leaving Sans and Papyrus with Arial.
Arial looked at her boys, "It's alright, as long as you're safe. You should go, I love you both." Papyrus grabbed Sans's hand and ran with watery sockets toward River's boat.
Sans looked back, "We have to go back! We have to go help her!"
Papyrus turned around and grabbed Sans's shoulders, "She's dead! Sans! She died! Because of you! You killed her! All because you just didn't trust our mother to do the one part of her job she's an expert at!"
Sans glanced between Papyrus and the dust covered ground, "No I…I didn't I…mom isn't…"
Papyrus pulled again, "We need to leave now." Sans let himself be tugged along. The two made it to Mel's house, who was nervously chatting to someone on the phone. Mel looked up as the twins approached.
Mel sighed in relief and spoke to the voice on the phone, "They just got here. I don't see Arial with them but the boys are here. Sans is covered in dust. Yeah, I'll take care of them for a few days." Mel dropped to their knees and hugged both boys tightly. Papyrus collapsed into their arms, sniffling from holding back tears.
Sans hung his blue hoodie up at the lab, tugging on a lab coat. Gaster turned to his son, "You're early."
The 17-year-old shrugged, "You told me five minutes early is on time and on time is late."
Gaster paused, "I believe I said fifteen. Still, I'm grateful you listened this time."
Sans pulled out some physics homework, "Can I work on this during the testing today since you wont let me help?"
Gaster nodded, "May I see it? Hmm…already talking about nuclear physics I see. Well, you've gotten most of these right. Fix one, three, sixteen, and…eighteen."
Sans took the page back and walked over to a desk, "Alright."
Gaster followed, setting a few papers down, "Could you work out the problems for these? We're calibrating the Core today."
Sans's sockets sparkled with excitment, "Really?"
Gaster nodded, patting Sans's shoulders, "If you want to. I'll check your work when you're finished." Sans excitedly worked out equations on a whiteboard nearby. Gaster smiled softly, walking to his desk. He examined the papers carefully, looking over each report. The Core was a project he'd been working on. Sans knew how important it was, seeing as it would power the underground. The current power system of just some generators were going to run out eventually. Some were already losing power in places like the Ruins. Though few still lived there, it was important to keep the lights on for those who did. Gaster perked up as Asgore entered the lab, "Ah, King Asgore. To what do we owe the pleasure?" Sans looked up from his papers, quickly taking the hint to go to a different room.
Asgore glanced at Sans before turning his attention back to Gaster, "Dr. Gaster, I didn't realize you had a son."
Gaster nodded, "Two, actually. They're both 17 now."
Asgore paused, "So, they were 11 when their mother passed?"
Gaster flinched, "Yes…they were. Anyway, what did you need?"
Asgore stopped a moment, gathering his thoughts, "I wanted to ask about your progress on the Core."
Gaster perked up, "Of course. I'm actually having Sans work on the calibrations now."
Asgore cocked an eyebrow, looking skeptical, "You're placing the lives of your scientists, our people, and the fate of the underground in the hands of a 17-year-old?"
Gaster quickly grabbed a few extra papers, "Of course not. I intend to check his work against my own and my colleagues. I have a lot of faith in my son. He's a bright child."
Asgore still didn't look convinced, "I see. Well, do you at least have the build schematics finished?"
Gaster handed the page to Asgore, "Here it is. I know it's rather large, but it has to power the whole of the Underground. I plan for it to run off lava, a synthesized substance, and ice to cool both before they're mixed. There will be walking paths, elevators, and such to ensure people can pass through safely."
Asgore nodded thoughtfully as he read over the directions, "I see. These plans all look very thorough. Good work. I'll start to look for workers to send your way."
Sans poked his head out of Gaster's office as Asgore left, "Was that Asgore?"
Gaster turned and nodded, "Yes. I'm sorry I've never introduced you two. There are things about him…trust me, you'd rather not know."
It should've been a normal day. The Core had been built and released. Sans and Papyrus were 18. They were graduating soon. Yet, Sans was curled up in his room crying. Papyrus nervously knocked on Sans's door, "Sans, I've heard you crying for an hour now? Do you wanna talk about it?"
Sans shouted, "Go away!"
Papyrus flinched, but never let go of the door handle, "Brother…alright. I'm here if you need me, Sans."
Papyrus walked around the forest, air biting his bones. He could've sworn he heard crying out here. The cries of a young toddler or baby perhaps. He'd come to check if there were any lost monsters. But so far nothing. So deeper in he went. There, curled against the Ruins door, was Sans holding something to his chest. Papyrus ran up to his twin, quickly checking over Sans and his HP. But it wasn't Sans who was crying. Sans looked at Papyrus, "We need to get them home." Papyrus opened his mouth to ask who but Sans parted his arms slightly. A shivering human toddler was in his arms. Papyrus was baffled, but quickly hauled Sans to his feet. Sans held the human tighter as he teleported the three of them home.