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.

Pretty self explanatory. This takes place after the Pacifist route in Undertale. Through determination, Frisk was able to bring back Chara, Asriel (Asriel is Flowey per say), and Gaster. I believe that Gaster is the father of Sans and Papyrus. I also don't believe that Chara is evil. The monsters are on the surface, and although they are amongst humans, most humans have accepted them.