Uncreated Undead

While most undead are created by deliberate Magic, it is also possible for undeath to occur due to a curse, or simply to long-term contamination by necrotic energy in the environment.
Cursed undead are created when a person survives for an extended period under a withering, or other curse which saturates their body with Necrosis. When such an individual dies, the necrotic energy concentrated in their body or soul animates them as an undead being such as a wight or wraith. Such undead are usually powerful, as individuals who attract such curses and survive them are typically remarkable in some way. The greatest curses produce such horrors as death knights.
It is also possible to simply absorb necrosis from the environment, should one be unfortunate enough to live in an area blighted with necrotic energy. This absorption is accelerated by acts of cruelty, and can be exacerbated by consuming food from animals or plants already contaminated. Cannibalism is especially effective at concentrating necrotic saturation, and is especially associated with the creation of ghouls and ghasts and other flesh-eating undead.
Necrotic saturation is also a circular affliction. The presence of these undead-in-potentia weakens the boundary between Aiaos and the Grim Plain. This in turn allows more necrosis to pool and results in an increasing number of contaminated individuals, eventually resulting in an atmosphere where strict funeral traditions are followed simply to prevent ghosts or zombies becoming the norm.
The greatest accumulations of necrosis in Aiaos are in the haunted relict of the Necropolis of Thosis, in the region of Zeras in southern Talahara, and in the-sacrificial centres of the Ophionic Empire.