Undertale: Believer

In a specific timeline, long ago, a few of the disbanded Human wizards that sealed monsters underground began a new group, secluded from the rest of the humans, moving in the shadows, never quite revealing what their plan was...

In the year 200X, the child of the leader of the wizards fell into the world of the monsters, the only parent she stayed with was her father, who had always treated her badly, however, her mother and her wife, whom she had cheated on the father with, because of his personality, she just wasn't happy.