From the Book of Seven Lords, Books 0: Book of Nightmares
The Mazoku are less numerous, but more individually powerful than the Dragons. The Mazoku reside primarily on the Astral Plane, their physical form, while still possessing actuality, being a sending or avatar of their Astral self. The advantage of this is that they can not truly be harmed by physical attacks, but likewise they are more susceptible to astral attacks.
Because of their purely spiritual nature every Mazoku is sustained by its belief in its own existence and importance. Consequently it is impossible for any Mazoku to place the existence and importance of another creature, disregarding their direct progenitor, above their own. To do so would diminish their importance and therefore, diminish their power and being. They are naturally egocentric and solipsistic; to a great extent their existence is shaped by their own perception of existence.
Due to their overtly spiritual existence Mazoku nourish themselves, not on material food, but on the negative and self-serving emotions of others. They are like empathic vampires, absorbing feelings of hate, bitterness, obsession, grief, lust, greed, fear, pride, self-satisfaction, pleasure derived at the expense or in spite of others, etcetera.
Contrary to common folklore their egotism is the only restriction of their range and depth of emotion. They feel as any other creature, sometimes with more depth due to their empathic nature and are not restricted to feeling only the emotions that men see as evil. It is true that Mazoku can not feel unselfish love, or charity for charities sake, because these are feelings which raise the importance of the continued resistance of others over the continued existence of the self. Pity, on the other hand, seems like an unselfish emotion at first, but actually comes from a position of self-importance, whereas self-pity is self-defeating. Joy, grief, desire, amusement, possessive love, disappointment, charity for the sake of being admired, Mazoku can feel all these things and more.