Grief could cause people to do terrible things. That's what Sans had reasoned over the long years. After all, when he had been a babybones, he had faint memories of his mom and dad laughing and smiling, full of warmth and light. It had only been after Arial died that things had started to go wrong.
"Daddy, daddy, look," Sans said, holding up the picture he had drawn. "There's you, and me, and baby Pap, and mommy has wings 'cause she's in heaven now."
Gaster took his head out of his hand, setting down the pen he was holding, and took the picture. He stared at it for a long time, then silently ripped it in half.
"No, daddy," Sans cried, as he ripped it again, and once more. Then he dropped the remains in the wastebasket. Sans went to grab it, but cried out as Gaster backhanded him across the face so that he fell backwards. Too stunned to even cry, he ran from the room.
The next morning, he woke to the sound of Papyrus crying. He ran into his brother's room, trying to see what was the matter. He tried making faces at Papyrus, playing peek-a-boo, everything he knew, but Papyrus still wailed.
"Shut up!" Gaster yelled from downstairs, and Sans jumped. Papyrus only screamed louder. Sans heard the scrape of a chair on the floor.
"I got it, dad," he called hurriedly. He ran downstairs to the kitchen and grabbed some milk out of the fridge, pouring it in a bottle. He ran back upstairs and stuffed it in Papyrus's mouth. Papyrus started sucking happily.
"Sans," Gaster called, sounding angry.
"Yes, dad," Sans said, scurrying down the stairs. Gaster was in the kitchen.
"Look at the mess you've made," he growled, pointing at the spilled milk on the counter and floor. "I will not have you wasting precious food."
"I didn't mean to," Sans protested.
There was a sharp sting of pain and Sans staggered backwards, clutching his left eye. He felt a strange, painful sensation in his soul, that he would later recognize as permanent damage to his HP.
"Don't talk back to me," Gaster growled, as tears sprang from Sans' uninjured eye. "Understand?"
"Yes, dad," Sans whimpered.
"Now clean that up," he said, and stalked from the room. Sans picked up a towel and mopped up all the milk, throwing it in the laundry when he was done.
The slightest thing could set their father off.
"Daddy," Papyrus said once, when he was older. "How do I tie my shoe?" Sans looked up in fear from the other room.
Gaster fixed Papyrus with an inscrutable stare as Papyrus held his foot up, hopping on the other. Then his eyes narrowed.
He raised his hand, but Sans got there first. Sans caught the blow, his head reeling and vision blurring as his hp dropped. Papyrus cried and Gaster growled, hitting him again and again as Papyrus shrieked, "No, no!" over and over again.
The next day, not sure himself how to tie shoes, Sans found an old pair of boots at the dump. He brought them home, washed them, and quietly gave them to Papyrus. He himself found a pair of too-big slippers to wear.
Finally Sans had had enough. Once Gaster had left for work at the Core, Sans ran to Papyrus's room, where Papyrus sat staring at the wall blankly.
"Pap," Sans mumbled, tugging on his hand. Papyrus followed unquestioningly.
Stumbling through New Home, Sans finally made it to the castle. If anyone could save them, it would be the king.
"King Asgore," Sans panted,reaching the flower-strewn throne room. He was dripping and shivering.
"My child, what is it?" Asgore said gently, taking in the tired youth with their heaving chests. Papyrus dropped to his hands and knees. His eyes narrowed as he checked them and noticed their low hp - Sans' permanently damaged.
"It's Gaster," Sans said.
"Your dad?" Asgore questioned, striding towards them. "Is he in trouble?"
"He's not my dad," Sans exploded. He hadn't called him that in a long time.
Asgore looked at the teen, taking in the powdery mark on his bones, and understood. His face darkened.
"Wait here, children." Taking up his trident, he walked out the door.
The Queen came from the next room. "Oh, my poor dears," she said, wrapping them each in a very furry hug. Sans stood rigidly, but Papyrus clutched her and started crying.
Distracted by the younger skeleton, Toriel didn't notice as Sans slipped away.
Sans followed Asgore at a distance. The king's cape billowed behind him as he marched determinedly through the underground. Monsters jumped out of his way, seeing his brooding stare and purposeful walk.
They arrived at the Core. Asgore stalked in, coming straight up behind Gaster.
"Gaster," he growled.
"Your majesty," Gaster said, turning and bowing low, then taking a step back while still bowing as he saw the look on the king's face. He faltered, then said, "What - can I do for you?"
Sans hid behind a piece of machinery, and gasped as Asgore grabbed the neck of Gaster's lab coat and lifted him into the air with one hand.
"What have you done to your children?" Asgore roared, baring his large teeth as he did.
"Nothing," Gaster protested, but his lip curled slightly in distaste.
"Then why are there marks of dust on their bones?" Asgore bellowed, grasping the coat with his other hand and shaking Gaster like a sapling in a storm. "My children are dead! How could you commit such a crime against a child?"
Gaster clutched Asgore's wrists helplessly, and an ugly, twisted sneer spread across his face. "They killed my wife," he spat. "They are no children of mine."
Asgore spun, suspending Gaster over one of the guard railings, and fear flashed across the skeleton's face. Sans felt a sense of grim satisfaction.
"Not anymore," Asgore said, his voice suddenly quiet and cold. Opening his hand, he thrust Gaster out into the void. Gaster hung suspended for what seemed like several long seconds, then fell, his scream trailing off into nothing.
A mix of emotions swept through Sans, anxiety foremost. He wanted to see Papyrus. With a shwoop, he was suddenly in the throne room.
"Sans," Papyrus ran over, crying with relief, and hugged him tightly. Toriel followed, running frantically with her skirts in her hands.
"My child, you are alright," she breathed, sinking to her knees.
"Gaster is gone," Sans said blankly.
"Who?" Papyrus asked curiously. Sans looked down at him in disbelief, but there was nothing but honesty in the younger skeleton's face.
"My child, what are you talking about?" Toriel asked. "Asgore left and then …" confusion twisted her features, and a haze entered her eyes. She seemed to struggle to find words, then finally said. "We were worried about you."
Asgore returned. No one, including him, seemed to have any memory of Gaster. Sometimes, when Sans would ask a new monster, a chill would enter his spine, as if he was being listened to.
Years past, and though Sans could not himself forget, he started to move on. Asgore was everything Gaster had not been. He played catch with Papyrus, helped Sans with his homework. When Sans hid a test from Asgore, Asgore gently coaxed the truth out of him. Sans admitted, barely able to speak through fearful sobs, that he had gotten a "B." He cringed as Asgore came towards him, but was surprised as Asgore enveloped him in a hug.
"My child," Asgore said tenderly. "I don't care what grades you get. I care that you do your best and that's all." Sans cried long and hard in his arms.
Though there were no pictures or videos of them together, since working batteries seemed to never fall to the dump, they were truly a family. Sans began to trust the king and queen, and finally would leave a happy Papyrus alone with them as he wandered the underground.
It was in Waterfall that he first spotted them. They looked a little bit like the picture of Chara Sans had once seen. "A human," he breathed, and teleported to New Home.
"Dad," he called breathlessly. "I found a human."
Asgore's expression changed, a shadow of the one he had worn when he had first saved the boys all those years ago. Sans stopped, uncertain, and Asgore lifted his lips in a smile that did not reach his eyes.
"Do not worry, my child," he said. "I will take care of it."
It was hours before the human arrived. Hidden behind an archway, Sans watched as Asgore stood before the barrier, speaking in a voice too low to hear, then raised his trident.
Memories flashed before Sans' eyes, and he nearly cried out. He moved to spring from his hiding place, but Papyrus beat him to it.
"Do not hurt the human," Papyrus snarled, and Sans' heart plummeted. Papyrus had always been too innocent, too pure.
"Papyrus," Asgore said in a deep monotone, "go to your room."
"No," Papyrus said, standing his ground. "I will not let you hurt the human."
Events seemed to be replaying on a different stage with different characters. Asgore pushed Papyrus gently but firmly to the side. He raised his trident over his shoulder, then struck. A look of horror crossed Asgore's face as a plume of dust sprang up. The trident was lodged in Papyrus's ribs. He dropped to the ground, badly injured or maybe dead.
"No!" Sans thundered, sprinting for them. With a flash of his eye, he threw the now-blue Asgore into the barrier.
He rushed to Papyrus, and was relieved to see his chest still rising and falling. Then there was a cry, and a flash of red across his vision. He turned to see the human fall and their soul rise, gently rotating into the waiting cask in Asgore's hands.
With a wordless cry, Sans launched lines of bones at Asgore, but stopped as a large, furry hand fell heavily on his shoulder. Looking up and behind him, he saw the queen.
"Asgore," Toriel said quietly, her voice both edged and weary.
Asgore looked at her with an expression of mixed defeat and defiance.
"Come, my child," Toriel said quietly. Stooping, she picked up the fallen Papyrus, a small glow surrounding him. His breathing became easier.
"Toriel, wait," Asgore said, but he faded as they walked away.
Sans followed Toriel to Snowdin. There he stopped.
"Your majesty," he said, and Toriel turned to him with a hurt expression, "With all due respect, I think we would rather be on our own.
Toriel stared at him long and hard. "Yes, my child," she finally said. As she lowered Papyrus to the snow, he began to stir. Without another word, she turned and strode away. It was only then Sans felt the familiar burning sting of his hp dropping permanently. He felt weary, as though life lay heavy upon him. Turning to Papyrus, he helped his brother up, and together they walked to find a new home.