Seithr(魔素Maso, Magic Element), in BlazBlue is a substance that covers the planet. It can neither be seen nor smelled. In small doses, seithr is harmless to humans, but in larger quantities can carry very detrimental effects; one can become addicted and their body will deteriorate. During the Dark War, the Black Beast spread this seithr all over the world, in order to operate. Because of this, the Six Heroes taught the humans the secrets of the "Magus" in order to defeat the beast. Ars Magus was created to consume the seithr and utilize it as a source of energy.