Undertale by My Class

Many centuries ago as two races ruled over the Earth, Humans and Monsters as they have been livinh in peace in decades... But the two races broke up for unknown reasons as they fought the civil war, then years later the humans were victorious as the leader of humans sent out seven greatest sorcerers to seal the monsters with a powerful barrier inside Mt. Ebott, as the legend tells "If someone climbs and enter Mt. Ebott will never return." Until many centuries later in 2019, an young human girl name as Frisk enters the Mountain when she accidently fell over the hole by the vine as her new story have began.