(Underfell sans x reader (female)) UNDERCOVER

Preparations

          You were confused and had so many questions to what you were looking at. Your soul floated in your hands as you examined the glow of the two different colors of red and white. You knew your soul's original color was a clear diamond color but you were stumped by why the other half was red.

"Sans what happened to my soul, who did this?"

"hey i told ya not to panic and let me explain."

          He positions you on his lap to face him and put his hands around yours as your soul stayed floating in your palms.

"when gaster stole half of your soul and combined it with his and was about to take the rest of yours, you pushed him into one of my magic bones that was sticking out of the ground and impaled him and his soul including the half of yours he absorbed. before your soul shattered, i manged to perform a risky theory that i've had for years..."

"And what might that be?" I ask.

"...soul transfusion―it's a bit different from absorbing a soul like what gaster did."

You were silent for a moment but realization hit you hard.

"Sans is this part of your soul!?!"

He didn't answer and looked away.

"Sans look at me, is this part of your soul!?!"

           You began to worry for Sans' physical state and began to notice how tired he really looked. His hands were trembling as he slowly fell onto his back, you quickly put your soul back into your chest and got out of his embrace and cradled his skull in your lap.

"Sans! Are you okay!!??"

He mumbled in assurance that he was fine and just really tired.

"Now i'm going to ask you one last time, did you give me half of your soul?" I say softly.

"well i wasn't just going to let you die on me, sweetheart." He chuckles and smiles looking up at you from your lap.

"But you could've died, and what if it didn't work and we both ended up dying?"

"but we didn't." 

          You couldn't help but give him a small laugh at his comment, washing away your worries and his. You caressed his cheek bones as you both looked up into the sunlight that was coming through from the hole above. It looked so small but you knew how really big it actually was, at that moment it dawned on you how far you actually had fallen from there. The scenery was beautiful but it wasn't enough to distract you long from the thought of your soul as well as Sans'.

"I remember months ago Papyrus was teaching me about the differences between a monster's soul and a human's soul―he told me that all monster's souls are white, so why is part of your soul you gave me red? Shouldn't your soul be white?"

He shifts a bit in your lap and coughs.

"yes my soul is white, but part of my magic is now permanently bound to your soul which is why it's glowing red." Sans explains.

"But what about you? How will you survive with only half a soul?"

"...it's going to take a lot of time for me to heal. my soul will regenerate parts of itself overtime but it might not regenerate the entire half that i'm missing."

"Oh thank god, I was scared that you would slowly turn to dust." I say as I wiped a tear.

          You were still scared for Sans and feared that he wouldn't be as strong as he used to be and began to cry. You tears fell down onto Sans and lifted his hand up to wipe them away.