Demon

Demons (魔物, Mamono)(Not to be confused for the actual demon species that of course originates from hell but instead a classification that humans and animals go under when they go out of control and their eyes turn completely red) are animals whom without any intelligence and control over their strong mana, run rampant and become a dangerous creatures. However, in case of a human, they are called Devils (魔人, Majin). Devils rarely occur, but are far stronger than a normal demon. However, Devils have become more prominent since Oliveira von Schtradius developed a process for turning humans into Devils.

Appearance
The distinguishing feature of demons and devils are their red sclera.

Personality
Most demons and devils are creatures that are driven entirely by their uncontrollable desire to destroy everything in their path. According to Merlin, both demons and devils lost all of sense of reasoning.

Background
Demons appeared whenever an animal lost control of it's mana. It was initially thought to be impossible for a human to ever become a demon. This was notion was overturned by the emergence of the first ever devil. There are now devils who have retained their sanity and are able to think instead of being driven by pure instinct thanks to the experiments of Oliveira von Schtradius.

Chronology
Demons were first seen when Shin was hunting them in his youth.

Abilities
Demons are more powerful than their beast counterparts. Even weaker Demons are known to become exponentially more powerful once turned, requiring trained knights with the aid of experienced magicians to take them down. Some are even strong enough to overwhelm human armies. Devils, however, are in a completely different league. Displaying greatly enhanced strength, speed, resilience and magic power, enough to devastate the country and easily take out entire human kingdoms. Only exceptionally powerful magicians like Merlin, Melinda, Shin and members of the Ultimate Magic Research Society have been capable of killing Devils.

Trivia

 * Devils who have sufficient skill in controlling magic and retained their sanity can hide their red sclera by limiting the amount of mana they use.
 * Once the source of their rage is gone, the demons lose all sense of purpose; akin to depression.
 * Natural demonizing causes explosions. Forced demonizing causes no such thing. But the size of the explosion depends on the magic power the demon has
 * Given Strom's transformation was enough to destroy his property and vaporize the deceived villagers who killed his wife, it can theorized that if Shin fell down this path, his transformation would be similar in terms of destructive force.