After Frisk goes missing, Caitlin, Frisk's twin sister goes looking for her in the the last place she saw her. MT Ebott, the mountain of dark legends, she finds a necklace that belonged to Frisk on the ground. Just like Frisk, Caitlin tripped and fell into the Underground. Caitlin finds things she never knew existed.

You've heard the stories, of the mysteries of a man who guides lost ladies home by night legend says his voice is like a demon of hell and anyone who's ever approached him has died. One night you get lost and you uncover his real story

Warning! There is a chance that there will be spoilers for the pacifist run of undertale. I recommend finishing that before reading this. There won't be any spoilers for the no mercy run, so don't worry about that! Also, don't worry about anything NSFW/lemon if that's not what you're into-there won't be any of that here. You're a human that's fallen down into the underground. You've decided that you'll stay instead of going home after fighting Asgore and sparing him. Now, you had made some great friendships while in the underground-but one of those friends in particular was one you'd like to be a little more than friends with... Aaaa an X reader fic! I haven't done one of these before, but I hope you still like it!