Long ago there 2 rases ruled over earth humans and monsters the humans were victorious and sealed the monsters underground whit a magic spell... After thousands of years a human fell down they befriended the young prince and became the monsters new hope but after some time the human became ill and the young prince died after. The ex Queen toriel and the ex king asgore made a divorce and toriel locked herself in the ruins tge place we live in now after some time a new human fell and they died too by asgore's hands. 5 other humans suffered the same fate. You know whit 7 human souls we could destroy the barrier actually that was our goal... Before another human fell they slaughtered half of the monsterkind including the queen and the king they even struck down the most powerful person in the underground some speculate that the human even killed the reborned prince but no one knows for certain the only thing we know is that we must kill every human that falls here we don't want to escape the underground anymore because if a child can eradicate half of us why would we want to see more humans