[Undertale] Sans X Reader - Repeat, Eternally

Chapter 7 ~ Gaster, Of Secrets Uncovered

As you reached Snowdin, you realized that Sans hadn't made another appearance since you had solved about four of Papyrus' puzzles. Papyrus had been puzzled, no pun intended, as to where Sans was.

As you entered Snowdin, however, you heard that familiar chuckle.

"Congrats on making it past my bro. I still don't trust you."

"You've got it all wrong- I don't trust you." You smirked at Sans, who looked a little off-put by your remark. You ran ahead of him, and Gaster reappeared by your side.

[Would you like to hear about how monsters reproduce?]

"...Stop doing that!" You shrieked, which turned every eye in my direction. You quieted down, and walked forwards, fast.

[It's also partly how I made Sans and Papyrus.]

"You... made Sans and Papyrus?" Your voice was nothing more than a whisper. "You're their father? Why are you in my head?"

[Funny story, that.] Gaster seemed sorrowful. [Let me tell you a story. Once, a human fell down into the ruins, long before you came.]

"And who was this human?"

[I'm getting to that part. Be patient.] Gaster swiveled his head around. [This human had no name. However, they were broken. They didn't.... work... properly.]

Gaster walked through the snow, leaving no tracks. You followed.

[This human couldn't speak. Couldn't see. Couldn't hear. Couldn't react, at all. All of it's senses were dead. I had, of course, performed experiments on several humans already, but I had never seen anything like this.] He shook his head. [They were completely unresponsive to any of my treatments or touches. Sans and Papyrus were but children, frolicking playfully and rarely entering my lab. This was the first human they had met since their birth.]

You listened quietly, interested in their first encounter with a human.

[The human still responded to nothing, until one day, Sans found his way into my lab. He was a small child back then, but he began to examine the human. A small light entered the human's eyes, but dissappeared as quickly as it came. But still, it was there. It was a breakthrough. I had never tried taking the human's soul out of their body, even though human souls are strong. The human seemed so fragile, and broken. It wouldn't fight back, so I wouldn't do any particularly harmful experiments. But this reaction sparked yet another reaction into play; my own.]

[With how broken the human was, all I could do at first was inject it with small amounts of DETERMINATION. That would only make the fingers twitch. Still, the human had not a single thought in their head. It was like they were an empty shell, waiting to be filled. I soon learned how to puppeteer the body; strings of DETERMINATION here and there, a little bit of sleight of hand... and I could make the human dance. I could make the human sing. I could make the human look alive. But the human was still broken beyond repair.]

You feared the thought of being tossed around like a puppet.

[So, I took our relationship as doctor and patient further... and withdrew their soul from their body. I was shocked at what I saw. Their soul was in shreds. Only a hint of it remained. To attempt to repair such a thing would be insanity.]

[But science is insanity. I was fueled by my desire to fix. Fix the human. Fix the soul. Awaken the human. Save the soul.] Gaster continued, entranced by his own story. [And finally, I did the most insane thing in the world.]

He paused, for dramatic effect.

[I merged my own soul with the human's. Not in a way that would make me powerful, but in a way that would provide sustenance for the human's soul. Unfortunately, this left me weak, and my soul became a quarter of what it was. I knew I was going to run out of time. I spent my days with my children, and my nights working on a certain project.]

"But why would it run out?"

[Because the human was still taking. I needed to finish everything before they took it all. I needed to spend time with the ones I loved.]

[One day, I was doing my routine check-up on the Core. Unfortunately, I had a dizzy spell... and I fell. I fell the wrong way, and was split and spread across... time and space. That's the only way to explain what happened to me.]

Gaster glanced at you, seeing if you were still following. You were. He had... died...? Because of his weak soul...

[Why can you see me, you ask?]

[When you and I met, you were my patient, and I, your doctor.]

[I, driven by my need to help you...]

[And you, not driven at all.]

[You, broken. I, whole.]

[Your very existence sated my loneliness.  I gave up my life to fuel yours, and orphaned two sons. That was my fault and mine alone.]

[You owe me much, ______. You owe me everything you are. And now, you're spending the soul I gave you to save the Underground.]