What's A Villain Without A Hero? (Underfell! Sans X Reader)

You are (Y/N), Frisk's twin sister. You two were like peas in a pod. Until one day she goes missing. When you look for her in the Underground, a certain edgy skeleton catches your eye. Will that skeleton share your feelings, or will he fall for your twin? (Trust me, that does not feel good, your twin getting picked over you. That stuff can strike you deep.)