In preparation for the threat of the Demon King's army, Usato, a healing magician, travels on a journey passing letters to ask for cooperation from various countries. Usato and his group depart from Samarial, the land of prayer, and on their way to their next destination, Mirark, they find a walled city that is not even on the map.

Usato and his friends have entered Rest Valley, a city enshrouded in fog, and receive a warm welcome from the locals. Led by Mena, the innkeeper's daughter, this town is full of kind people, holds no discrimination against subhumans, and has a rich and cultural life, seeming almost like a utopia.

However, despite the tranquility, a secret is being kept hidden within the city.