Vampires don't consider those who misuse their power vampires; and demons too distance themselves from demons who misuse their powers, singling them out by referring to them as devils.
Like vampires, demons feed on energy [human lifeforce energy isn't necessary as long as other energies are available] in their astral form and in their incarnations on Earth. However, vampires have a body during incarnation on Earth; whereas, demons are within that body but not connected to it. Therefore, demons need to feed on energy to be at optimum health and function because they don't benefit from the energy human bodies naturally get from daily activities [eating, drinking, etc.]. Demons do eat/etc. when incarnated on Earth, but they don't extract energy from doing so.
Since demons aren't too connected to bodies, they feel somewhat detached from society, allowing them to come up with solutions to situations that are unbiased and the most beneficial towards the greater good. This predisposition of demons is useful for making and implementing decisions without time to prepare. Demons can do this because they selflessly leave personal opinion and emotions out of logic, law, and ethical standards.
Demons are partial to watching individuals being happy and to making hypotheses regarding the nature of non- demons. Resultantly, demons tend to change their plans unpredictably, moving to different cities and changing bodies in order to get a more accurate portrait of the nature of non-demons.
Similarly, demons tend to use the word "shapeshifting" to refer to their phasing in and out of different personalities.
Although demons are selective in who they give assistance to, emanate negative energy [irritability, cynicism, stubbornness], and only experience good luck when they take that lucky chance from someone else, they are by the same token fiercely passionate, brutally honest [often empathic], and wildly imaginative [Romantic!]. The keys to maintaining friendship with a demon are strictly obeying the demon's moral code [expect all of the codes to be extreme-since demons think in terms of logic or sentiment but not mixing the two-and several codes to be thoroughly ridiculous], constantly coming up with things that surprise the demon [that shows that you continue to care], and tracking him/her down like a detective on a regular basis any time of the day whenever the demon is upset.
Demons remember pieces of the past and of their existence in the astral realm. I don't know the story, but based on what several demons have told me, this is the story as I have come to understand it:
There are several dimensions in the astral plane, and they're each pure unconcious energy [so obviously no light either]. Eventually, the energy mass starts to gain conciousness and subsequently concious lifeforms come out of the mass. These lifeforms wander around their dimension then into other dimensions, picking up knowledge. That knowledge builds into personality [a soul].
There was a supreme being [god] that ruled over at least one dimension [perhaps more than one, possibly all] and he/she was a concious energy mass that oversaw a balance and order for his/her dominion. From the supreme being, came concious lifeforms that were what we call angels [A lot of demons consider angels to be just and loyal but at the expense of passion and other extreme feelings that cause chaos.]. A concious mass came to be that chose to tread the path of extreme emotions, and was shunned by the supreme being from his/her city of silver [where he/she and the angels plan/planned the designs for the rest of the dimensions or for at least several dimensions]. In the aforementioned dimension [and possibly in several or all dimensions], what one thinks of materializes; and so the chaotic mass in a bout of anger created what we call Hell, and went to live there, and from him/her came concious lifeforms of like-mind to he/she, which we call demons. The city of Heaven and the city of Hell continued to expand, and eventually expanded into the dimension where planet earth is. Whether they're still expanding or not, the angels are an inter-dimension police force. That can come in handy because concious lifeforms visiting dimensions that they aren't from can be trapped in a land of illusions by resident demons looking to feed on the energy charged with the emotion fear. Angels work together to perform collaborative tasks and demons work together [sort of] to perform collaborative tasks.