A realm of power is a category of supernatural influence. There are four realms in Mythic Europe. The Divine realm, which encompasses the creatures, things and areas of the divine, as well as the power of the divine in its various forms, as well as areas inhabited by worhsippers of the divine in any of its forms. The Infernal realm encompasses the creatures, things and areas of the infernal, as well as the power of the infernal, or those forces that work against the Divine. The Faerie realm and the Magic realm are believed by some to have been a single realm that split apart long ago.
Whatever the history, the Magic realm encompasses those creatures, things and areas that inherently have power on the Earth. The power of magic is seen by most magi in the Order of Hermes to reflect being closer to the Platonic forms, to be truer representations of what a being or thing is. Generally, the magic of a creature of this realm is not dependant upon any form of worship, belief, divine grace, or infernal damnation.
In this latest 5th edition of Ars Magica, however, the creatures of the Faerie realm are essentially living stories. They crave participation by humans in their stories, though most faeries are not aware of this sustenance. Participation need not be apparently beneficial to any particular faerie creature. An individual dragon may draw whatever magical sustenance that faeries crave from being vanquished by a human as well as from terrorizing humans.