After Frisk left the underground (neutral ending), Toriel returned as queen and ruled the kingdom in Asgore's place, and also introduced other policies... But those policies faced opposition from all the monster residents, who were very depressed and disappointed after Frisk left and left behind many losses, they want to kill all humans who fall here in the future to avoid disaster.

(At this point it was long after Frisk A sinistra, eri un essere umano [indipendentemente dall'età] che è caduto sottoterra ed è stato portato davanti a Toriel per il giudizio 'Non preoccuparti, il Toriel non ti ucciderà')