you are a human-(skeleton) moster hybrid living on the surface (after the true pacifist ending) after escaping from an abusive orphanage and living on the streets for around a year, you run into two skeletons...
You're a human girl, living on the surface with Frisk, who is your younger sibling. You one day find two children, who's been chased away from neighborhood to neighborhood. And with you're kind soul, you couldn't leave them to live in the streets. You take them in, and meet their father. But will one day, lose them, because of a war.
There is some ErrorBerry, and PaperFresh in this too.