In the world of Cradle, vital aura gathers around the elements it belongs to; for instance, stone aura gathers around stone, and water aura gathers around water. The more of an element that is present, the more aura gathers there. Slowly, and at different speed for different elements, the elements themselves will start to gather the aura, and if left undisturbed for long enough, these veins of vital aura are refined into a higher state. Pools of water will turn into sacred pools, which are often used to refine elixirs, and Titan's Bone, which comes from stone, is almost unbreakable.
aura into madra
Madra comes from vital aura in the environment. Madra is spiritual energy. Sacred artists use madra throughout their lives.
A baby is born with pure madra. A infant’s life aura, blood aura, and dream aura are converted into pure madra. This occurs at birth and during early childhood, but as vital aura is gathered from the environment and integrated into the core, the core takes on the aspects of that aura, and the corresponding madra is produced instead. For example, Orthos and Lindon can cycle destruction aspects of aura and fire aspects of aura from the environment, if fires are burning somewhere, and convert it into the madra aspect that fuels the Path of Black Flame.
Once cultivated, madra can be used to fuel and empower a multitude of techniques as well as one's own body. As sacred artists advance, their madra becomes more potent and more dense, allowing them to do more with less. See Advancement Level for indications of how much madra is required per level.
The core resides in the center of one's spirit, placed just below the navel. Madra channels loop throughout the body, to and from the core. Replenishing and expanding the madra pool of a core is done through cycling, drawing in vital aura of the same aspect, or through the use of elixirs and pills.
Hunger aura is different. It’s not a natural phenomenon. It’s not a vital aura. According to Subject One,
"Hunger aura is not a natural force. It is a corruption of the natural order of Cradle. A manifestation of ambition, of selfish desire, created by the presence of Monarchs.” It corrupts. Long ago, before intervention, “hunger aura drifted all over the world, and where it moved, all other aura weakened. It corrupted everything; Remnants, natural spirits, sacred beasts. Even humans...When your body and your spirit have both grown too great for this world to contain, you must escape to a place that can contain you.” (Reaper, ch 21)
But hunger aura is converted into hunger madra. See Subject One, who is called The Father of Hunger Madra.