Demon beasts are a dangerous kingdom of creatures. They take many forms, and seek to kill and destroy all that they can.
Demon beasts have preyed on humanity for centuries. In order to defend against them, humans developed Silhouette Knights, massive suits of enchanted armor that can be piloted to fight against them. The kingdom of Fremmevilla is the human country tasked with defending all intelligent species from the demon beasts, as they are on the border of the Great Bocuse Forest, where the demon beasts originate.
Demon beasts also contain Catalyst Crystals, a type of gemstone which can convert ether into mana. These Catalyst Crystals enable them to use magic, as evidenced by the behemoth breathing fire. The Crystals can be reshaped into Ether Reactors, which are then used to power Silhouette Knights.
The demon beasts are mainly loners, although packs of demon beasts have been seen before.