Gaster AU x Reader ONESHOTS

WD Gaster x Sacrificer! Reader

You and Frisk ran with all your strength. Undyne was chasing you both for one of your souls. Your arm was already broken and you had a limp. You and Frisk made a sharp turn and hid behind a rock. Your sweat rolled down your face as you got an idea. "Frisk," you knelt down and gave Frisk a picture of you both, "never forget." Frisk had tears going down (his/her) eyes as you kissed their forehead. "I love you." Frisk wrapped thier arms around you and signed I love you too before running towards the path.

You stood up and ran towards Undyne was. You saw her looking at Frisk. "Hey! Fishlips!" Undyne looked at you. "OVER HERE!" You ran as Undyne chased you. You were much slower since you didn't have Frisk helping you run. Before you knew it, you were stabbed and killed. You woke up in a black space. "You saved your (sister/brother)'s life... why?" You looked at a skeleton like figure. "It was (his/her) idea to save the monsters. I think (he/she) should live that dream." You answered as you stood up and leaned on your good leg. "I see."

"I am WD Gaster, former scientist and creator of the core." Gaster said as he seemed to have taken a bow, you took a bow while saying "I am (y/n), former sister of Frisk and inventor." You both smiled before you noticed the black area melted to the barrier room. You saw Frisk connecting your soul to a heart locket and (him/her) ready to fight Asgore. "Can Frisk see us?" You asked, Gaster shook his head before you sighed. Gaster noticed and placed his hand on your shoulder. You noticed a circle was in the center. "It's ok."

You looked at Frisk and saw (he/she) was dodging and trying to spare Asgore. Gaster saw you smile and mouth 'that's my (brother/sister)'. Soon, you and Gaster watched as Asgore accepted Frisk's mercy and even defended them against Flowey. The two of you watched the whole gang, including Flowey, cross the barrier. "You may go." You looked at Gaster, "Frisk has your soul. You can follow (him/her)." You shook your head and smiled. "I know Sans will protect (him/her). I'll stick with you." Gaster smiled before the two of you went to the waterfalls and sat to watch the stars.