(You are a Sans.) You'd been in a particularly rough genocide run in your au when the human decided not to finish the run and just reset the au. You wake up in your bed and feel a wave of relief hit you. You get up and fall through a black portal that seemingly came from nowhere. You hit what feels like the ground as the portal closes behind you. You stand up and look around the pure black void for a moment before getting surprised by a very cheerful voice behind you.

S Gaster: "Hey, someone fell into the void! Hello there, unknown skeleton!."

You turn around to see a very exited version of Gaster standing on the porch of an oddly normal house and waving enthusiastically.