Do Your Creepy Face

You find a file. It's a video marked "Surface Day year two", but so is the file next to it. That one seems to be a good size, maybe an hour of recording, but this one is much smaller, and it's thumbnail is pitch black. Out of curiosity, you click it.

(Post-Pacifist. Chara and Frisk have come to an understanding and share Frisk's body.)