Handplates: When The Walls Crumble (Gaster x Reader)

Based on Zarla's comic series, Handplates.
You are one of the head scientists of the Underground. You work for King Asgore, and Alphys is your assistant as well as your dear friend. W.D. Gaster is also a dear friend of yours, but lately, he has been acting strange. Neither of you know why.
One day, you finally get an answer.
Set in the strip, "In an isolated system."