Frisk was lost while playing near the mountain. No one knows they fell into the sealed monster world. The rescue comes in the face of a kind sheep Toriel, who mothers the kid as her own.
Though harmless at first, your character can hide beneath layers of mysterious armor and equip a sharp weapon. They can point a sword against their friends and scare away local monsters. Your villain can grow in power and crush the whole game.
Or, you can thank Toriel for her help and go explore the unknown world. You can chat with monsters and undead about their living and solve conflicts peacefully. Because you know that you’re a novelty in their place, and no one really wants to hurt you. In short, choose any route on the crossroad and unfold a beautiful—or ugly—story.