The Calamity Valley, according to what Fruity knew from his past self, is a region—or more like an entire continent—in the Tormented World, where various kinds of monsters live. In this world, the monsters are referred to as Demons.
Although he doesn't have all the knowledge, the little he does have is enough to inform him that the monsters in this world are more sentient than those in his own world.
When they grow to a certain stage, they can take human form and communicate as humans do. However, although they can take human form, they retain some of their monster features, making them distinguishable from humans.
This also means they are intelligent creatures, and because Fruity knew the knowledge he had was probably outdated, he started his journey with his full strength restored. He had become a Saint, which meant he had formed his Star Core, but he still hadn't saturated it enough to advance to the Sage Stage.
