You just got from the future and found yourself in a cave like area. You get up to look around to see a skeleton and a human girl by the age of 15 looking at you, it seems you spawned in between them

Sans: "uhh... heya, new kid."

Frisk: You greet the person that poofed in between you and Sans without questioning a thing

Maybe they could help you fix your future(Your time period) and rid it of "The Thing"