Death Magic, also known as Necromancer, is the art of resurrecting the dead and manipulating the forces of life and death via forbidden arts, creating Undead in the process.
The individual that commands this ability can unleash the reanimated corpse as a flesh-craving monster or simply opt to manipulate the corpse remotely. This art is seen as morally questionable and as such is actively suppressed in most nations of The Continent and it's even illegal in the Magic Kingdom of Zeth.
It can be learned of during one's lifetime, but to actually use the abilities, one technically has to be dead or to have experienced death in full.
The AL Church preaches that Death Magic is a terrible sin, and encourages followers of the faith to devoutly purge anything to do with it. Priests of the AL Church are looked at with more respect and honor if they successfully banish the undead and those responsible for them. As such, those who wish to elevate their status or simply wish to stay true to the AL doctrine ruthlessly hunt down anything related to Death Magic.
Even kind-hearted individuals like Sel Catchgolf can become hotheaded and radical in the pursuit of the undead. Some Divine Magic spells such as Purify were created solely to combat the horrors brought about by Death Magic. Death Magic was actually created several hundred years ago as an "unintended by-product" of Freak Paraffin's research.
Learning from this, Magic Master Rune developed his Biometal as an offshoot of this form of magic.