Gaster sat on the couch for some time, just hugging Sans.

He felt like his Soul was going to break.

That Sans, that his son had gone through that, had suffered so much. That he had been broken.

It was unthinkable.

And yet, it had happened.

"d-dad?" Sans' voice was muffled, as his face was buried against Gaster's shoulder.

"Yes?" Gaster's voice wavered just a little.

"i- ... i appreciate the sentiment- ... but my ribs are still a little bruised."

"Oh. Sorry." Gaster loosened his grip on Sans a bit, but didn't let go.

Sans seemed perfectly content to stay there, too.

They probably would have stayed like that for longer if Gaster had not felt his phone vibrating in his pocket.

He released Sans and pulled the small device out of his pocket. Recognizing Papyrus's number, he lifted the phone to his skull.

"Hello?"

"Dad?" Papyrus's voice was just a bit concerned. "Are you at the lab?"

"No."

"Did you forget to go again?"

"... Yyyyyes...?"

Gaster had the good sense to jerk the phone receiver away from his skull as Papyrus let out a frustrated shout, loudly proclaiming his family's laziness. After a couple minutes, he calmed down.

"Okay. I'll be home in a few minutes."

"Alright, Papyrus. See you then. Love you."

"I love you too, Dad, even if you are lazy."

Gaster just chuckled as Papyrus hung up.

~o0o~

A little over eight minutes later, Papyrus burst excitedly into the house. In the eight minutes it took for him to walk from the lab to the house, he had forgiven his father and brother's laziness, more or less forgotten about it, and become excited again about the news he had heard that day, and planned to tell his family.

"Dad! Sans!"

They were both in the living room, on the couch, looking at him.

"hey, pap. s'up?"

Papyrus slung off his backpack and rifled through it a minute, before pulling out a neatly folded newspaper and thrusting it towards Gaster.

"Look! They're saying that all the Corrupters were chased out of Waterfall, and it's safe to go in there again! Can we go, Dad? Can we?!"

"Now hang on a minute, let me take a look at this..." Gaster unfolded the newspaper with a flourish, and began to read. Sans also leaned over and read it over Gaster's shoulder.

After a minute, Gaster peered over the top of the newspaper and peered at his younger son, who had fallen silent, but was still bouncing eagerly on his toes.

"... Do you have any homework to do?"

Papyrus nodded. "Yes, but once I finish it, can we go?"

Gaster sighed and nodded. "I suppose so."

"NYEH HEH HEH HEH!!!" Papyrus laughed eagerly, and grabbed his backpack, running into the kitchen to do his homework at the table.

After a moment, Sans rose off the couch. "guess i'll go see if he needs any help with that."

A few more seconds passed before Gaster followed his sons into the kitchen.

~o0o~

While Papyrus was thoroughly excited to be in the now Pure-controlled Waterfall, both Gaster and Sans had conflicting feelings about the place.

On one hand, they had many happy memories of the place before it had been a warzone, like the time before Sans had gone to fight, when Gaster had brought a telescope into one of the caverns, and they had spent the day there, looking at the "stars." Gaster had pointed out all the "constellations" in the ceiling of the cavern, as well as told them about the real sky.

That had been a good time.

On the other hand, they both remembered the day the defenses in Snowdin finally failed, and the Pure had to fall back to their base in Waterfall. They both remembered a good many monsters who had been turned to dust or captured and corrupted that day, and in the days after.

But, Papyrus was happy to be romping through the wet caverns, rediscovering things that had been lost to him for more than five years. Sans was happy because Papyrus was happy, and both of his boys were happy, so Gaster was happy.

Eventually, after crossing a series of bridges, they came to a large cavern filled with tall grasses and reeds, a couple of small, shallow, glowing streams running through it.

"heeeeeey," Sans said, a note of excitement in his voice, "i remember this cave! this was where i fought for the first time!"

"Really?" Papyrus looked at his brother, and Sans could practically hear him begging for the story.

"yeah." He looked to Gaster. "you brought lunch, right? why don't we eat here, and i can tell you guys."

⎰Prior to This...⎱

It was a Big Day for Sans.

Yesterday, Gaster had finally decided Sans was ready to go into combat. Now, the pair were almost to the Waterfall camp, where Asgore currently was (for morale), so that Gaster could finally show the bossmonster the weapon he had been working on for the past fifteen years.

They entered one of the smaller buildings in the camp. Inside, after a small lobby area, was a conference room type setup: a large table surrounded by chairs. Asgore was standing in front of the table, wearing his full battle regalia, cape, crown, armor and all.

"Ah, doctor." He smiled warmly at his Royal Scientist. "It is good to see you."

Gaster grinned, but Sans could tell he was nervous about something. "Your Majesty." Despite the fact that they were speaking in the Common language, Gaster's hands still fluttered slightly in front of him, signing in Hands.

Asgore looked friendlily at Sans. "And who is this? Another of your assistants, come to help you?" He offered a large, furry paw to Sans, who shook it.

"Well, that, and my son..." Gaster trailed off, hesitating, but Asgore didn't notice.

"Son?! Why, Dr. Gaster, I did not know you had a wife!"

"Well, I don't-"

But Asgore wasn't particularly paying attention to Gaster. He was talking to Sans.

"Imagine, the doctor's son! I did not think that would ever happen! So, what is your name?"

"sans." Sans answered, the edges of his grin turning upwards. The king was friendlier than he had expected, despite the many stories he had heard. "comic sans gaster, if you wanna be formal."

"He's-" Gaster tried again.

"Sans!" Asgore laughed. "I think it fits you! And you are also your father's assistant, come to help him show off his latest weapon?"

"He is the weapon." Gaster blurted out.

For a moment, Asgore was silent.

Then he looked at Gaster, a slow frown crossing his face. "What do you mean, 'he is the weapon'?"

Gaster hesitated, opening and closing his mouth, but saying nothing. His hands were similar; Sans could Speak quite fluently in Hands, but the gestures Gaster was making made no sense.

Asgore prompted Gaster again. "Doctor, you promised to stop the experimentation on live subjects. Only the integrated weapons, you promised."

So. That was why he was so nervous.

Gaster's shoulders slumped. "Yes, I know-"

"And on your own son, no less!"

"... Technically, he's not my son, he's my clone."

"... What?"

Gaster raised his hands in response, showing off the holes in them. Then he continued. "I know I promised, but just listen. Asgore, we need something stronger than what we have, and I knew how to do that. So, as I couldn't get test subjects, I cloned myself, and intended to use them for the experiments. But then they-"

"They?!"

"Yes, they. Papyrus is Sans' younger brother. Yes, he is another clone, no, he is not a weapon. Anyway, after a few years, Sans grew up enough for me to start work, but, unlike I had originally intended, he was more than a frame capable of obeying orders; he was a fully sentient monster. He even helped me with the experime-"

"Gaster-"

"hey," Sans interjected before things got too heated, "he told me what he planned to do before we did it. made sure i fully understood what would and could happen before i agreed to help."

"You agreed to this?!"

"... okay, admittedly, he never told me it was illegal. although, he did make me keep it secret. i guess that shoulda been pretty obvious, then."

"Sans, that's not helping me!"

Things just went downhill from there.

"Doctor, how can you expect him to logically-"

"-but i wanted to help, and-"

"- never did anything without his consent! And now he's probably stronger than-"

"- doesn't even look like he's a teenager-"

"-and could probably beat Commander Gerson and Captain Undyne at the same-"

"-fifteen years old, thank you very-"

"Your Majesty!" They all stopped as the door was slammed open by a messenger. "There's an entire platoon of Corrupters storming the northwest caverns!"

The messenger went on a little more, but Sans and Gaster were talking amongst themselves.

"This is it, Sans. Are you ready?"

"i mean, i guess so."

"You don't seem very enthusiastic."

Sans gave Gaster a quick glare. "of course not. this is the first time i'm actually gonna be in danger."

"But this is what you've been talking about for the last six years!"

"yeah, but i still wasn't in any danger!"

"-you two listening to me?"

They both snapped back to attention as Asgore lectured to them. "Do I have your attention now? Good. Listen. You are going to stay here. You are not going to engage in combat. And when I get back, we are going to have a very serious conversation about this."

"but-" Sans started.

Surprisingly, it was Gaster who cut him off. "Sans." Sans could see Gaster's anger, and decided to not look at Gaster's hands, but fell silent.

Asgore nodded. "Good. I will see you later." And then he left.

Sans turned to Gaster. "dad! why did you-"

"Shh." Most of Gaster's anger had vanished, and he had that rare wicked gleam in his eye that Sans recognized from the few occasions when he was pranked.

Sans understood. "ah."

For a moment, they just waited, listening to the commotion outside as soldiers got ready for combat and marched off to face the enemy.

Then Gaster turned to Sans. "Well then." He was grinning. "We have some lives to save. I assume you know a shortcut?"

Sans grinned. "yep." He offered Gaster his hand. "follow me."

Gaster took his hand, and together, they walked out the door, and into a warzone.

Well, it wasn't actually a warzone yet.

They were standing behind the ranks of Pure soldiers, assembled in the cave in a defensive position. Asgore and Commander Gerson were at the front of the defensive wall. Some distance down the hall, the shrieks of the Corrupt Language could be heard.

Sans turned to Gaster. "i assume you're staying here?"

Gaster nodded. "Mmhm."

"okay, then, guess i'm going."

"Alright. Make me proud. Do my reputation justice."

Sans chuckled, and turned to start making his way through the crowd of soldiers.

After a good three minutes full of "'scuze me"s, "pardon me"s, and "comin' through"s, Sans reached the king and commander.

"so," he grinned up at the two taller-than-him monsters, "how many of 'em do ya think there are?"

They both turned to him. Gerson looked perplexed, and Asgore mad.

"I thought I told you to stay there!" Asgore spluttered, gesturing with his trident.

"hey, don't sweat it. i have a habit of disobeying people when i know i can do something better. call it a family trait."

"Who's this?" Gerson let the massive golden hammer that was his weapon drop against the ground.

Down the cave, the noise of the Corrupters got louder, and the tunnel certainly looked darker.

"th' name's sans. comic sans gaster, and i'm here to save the day."

And with a wink of his left eye, Sans took a quick shortcut to stand about twenty feet in front of the Pure troops.

The Corrupt exploded out of the dark cave, heading straight for him.

Time seemed to slow.

Sans took a deep breath and closed his eyes, readying his Magic.

One.

Deep breath.

Two.

Pull up the Magic.

Three.

Exhale

Four.

Slow pulse.

Five.

Fight.

He snapped open his eyes and twisted to the side as a Corrupt attack shot through the space he had been standing in mere seconds before. In the same swift movement, he lifted his left hand, loosing the devastating beams of the Blasters he had summoned.

And then the battle was on.

Sans leapt and dodged, summoning bones and Blasters and dodging nearly everything that came his way, and was barely phased by what did hit him.

And then he saw Asgore and Gerson, back to back, surrounded by Corrupters. They were doing a pretty good job of defending themselves, but as the battle seemed quite well-tipped in the Pure monsters' favor, Sans saw no reason why he shouldn't help them out a little, and show off at the same time.

So he took a shortcut, landed right behind a Corrupter, and ran it through with a bone. It had hardly begun to turn to dust before he was onto the next, summoning a Blaster and blowing it to oblivion.

And then he got hit from behind. Hard.

HP: 652/900

Really hard.

He climbed to his feet, ignoring the ache in his back, and turned to face his attacker.

It was a large monster. Multiple... limbs, all eqipped with a Corrupt attack waved at Sans, almost tauntingly.

Sans' grin turned devilish. "oooooh, you're gonna regret that."

He lunged forward.

In a matter of seconds, the both of them were so deeply engaged in combat that they hardly noticed their surroundings.

Sans leaned back in an almost Neo-Matrix-style dodge to avoid two Corrupt attacks, then summoned a wall of bones to block a third, only to be hit by a fourth. Meanwhile, the Corrupt monster blocked a quick barrage of bones, then got hit by a Blaster.

They continued like this for some time.

Then, finally, Sans decided the Corrupter had to have low enough health by now, and it was time.

He took a small shortcut to stand just out of reach of the Corrupter's many limbs.

Time seemed to slow again. Sans counted off again, slowing his pulse.

One.

Deep breath.

Two.

Dodge an attack.

Three.

Exhale.

Four.

Blue, blue and yellow in his sight.

Five.

Fight.

He ducked his head and thrust his hand upward with a guttural roar. The monster's Corrupt Soul became outlined Blue against it's chest, and it shot upwards, into the waiting bones that shot out of the ceiling overhead.

Black dust drifted downward.

Sans looked around.

The Corrupt had been all but defeated, the few remaining alive fleeing.

Gaster walked up to him and set a hand on his shoulder. "Good job."

Sans grinned up at him. "thanks, dad."

"Of course, you only have me to thank, as I created you and gave you your weapons and-"

Sans punched Gaster lightly in the ribs. "ha ha, very funny."

Rubbing his side, Gaster just chuckled. "Anyway, what do you think our odds are of getting some food from the mess hall? I mean, we aren't technically soldiers, but from the looks of things, you could really use some healing items."

Sans took a look at his HP.

HP: 98/900

Then he looked up to where Asgore and Gerson were walking towards them. They both looked impressed.

"i'd say our odds are pretty good."

⎰Present Day⎱

"and so," Sans wrapped up his story with a flourish of his hands, "they made me commander."

Gaster snorted. "They did not just make you commander then and there. It took another three and a half years."

Sans shrugged. "still. that's a lot faster than most people get promoted."

They were sitting in a reasonably dryish section of the field in the cavern, and had finished their lunches some time ago. Papyrus had been listening to the story, enraptured. If anything, today had only increased his awe of his older brother.

They stayed there a little longer, before Gaster said it was getting late, and they had to go if they wanted to get home before dark.

So, they stood, and began their trek back to Hotland.

§

A/N

D'you guys wanna know what's really awesome?

Like, really, REALLY awesome?

Okay, I'll tell ya:

You guys. Each and every one of you readers.

Seriously.

This book is at 1.5K reads. Almost 200 votes. And nearly 400 comments.

Every time I get on Wattpad and see that I have a notification, wether it's a vote, or a big, long comment about the chapter, or just someone stopping in to say "hey! This is cool!", every single time I get a notification about UnderCorrupt, I grin like Papyrus does when you tell him you love his spaghetti. 

And, thanks to all you guys, I'm grinning like that quite frequently.

Thank you.

Thank you so, so much.

I love you all.

...Platonically. 😉