Despite the name, a demilich is not a lesser lich, but rather a lich who has evolved beyond a need for its undead body. Great wizards and sorcerers usually become liches in order to continue their pursuit of magic and power beyond death. Demiliches are those who are close to reaching the end of their arcane journey; who understand the nature of magic and reality in a way no mortal could conceive.
A lich becomes a demilich when they no longer need to be continually tied to a body. The lich must somehow learn the art of creating soul gems and replace eight small pieces of its body with them. Often the soul gems become jeweled eyes and teeth in the demilich’s skull, but they can also become joints in a hand, or discs in the demilich’s spine. Once the power of the lich is focused in one part of its body, the rest of its skeleton crumbles away. The part that remains contains the soul gems; the eight gems act as the demilich’s phylacteries.