Demons, also called Devils are malevolent spirits who are often associated with or known as Fallen Angels, especially in the Abrahamic religions. However, in fiction Demons can be any number of malevolent beings normally possessing supernatural abilities and influence over different realms and dimensions that put them somewhat higher in scale than your average monster. They often corrupt, possess or destroy the innocence of others. 

IMPORTANT NOTES:

• Demons originate from spiritual and/or alien realms that are evil in nature. That means that most of them only know how to be evil, and cannot understand what is right or wrong.
  • Humans that die and become agents of Hell or similar realms are to be listed under Damned Souls even if they gain demonic powers.
  • Evil deities or cosmic entities are not necessary Demons unless the story made clear they came from evil realms.
• They can only be Pure Evil if (while meeting all criterias) their Moral Agency has been made clear, as seen in the case of Valak and so on.
  • Although, there are some Demons that can show redemption as not all Demons are truly evil despite their frightening appearance, such as Sesshomaru for example.