Deimos are a generalized group of many subsets of races. Deimos are described as "monsters who can use tools" making them very humanized monsters. They also are known for their ability to use magical abilities making them desire the resource known as Spirit Stones to help aid in their survival.
The Deimos are a very powerful group within the Arc The Lad Series. Many of their sub species having control over large settlements including Rueloon, Orcoth and Drakyrnia. Many of these large settlements were used in war efforts against Humans and amongst themselves,most notably the constant conflicts between the Drakyr and Orcon.
The Deimos species as a whole are one that is simply trying to survive. Their hatred of Humans comes from their taking of the Spiritual Stone resource one of which the Deimos rely on heavily for their magical abilities. They justify every action they perform as an act of survival. However, some are seeking revenge Volk, the last known living member of the Lupine tribe has deep rooted hatred for Humans because they are the cause of the death of his family and subsequently the fall of his race.
Darc who would become later known as "The King Of The Deimos." Was the Deimos who would eventually help shift this ideology, once a Deimos who was on track to have the Deimos survive forcefully by killing off Humans would eventually come to the conclusion that a peaceful resolution was possible, after coming to a resolution with his own human brother Kharg. The Human and Deimos races still highly disagree upon each other but have put their Waring tendencies aside to seek a more peaceful ideology.