Ghost

The principle behind ghosts in the Overlord world is scientifically complex but when boiled down is quite simple. Rather like organ donation on Earth, when they come of age the people here have the option of being fitted with a transfigural neurologics spell, so that if they die they are automatically transfered to a phantasmic energy crystal. The spell is designed to hold neural patterns for up to a decade, after which the pattern will degrade and the individual will disappear. A few spells can extend this longer, under the right circumstances, but most ghosts opt out once their decade is up.
This effect is useful for two reasons. First, if the person’s death is unusually abrupt, it is now possible for them to handle their affairs and wrap up any outstanding business. And second, if the person’s friends can somehow obtain a resurrection device, reverse transferal is possible, allowing the deceased person in question to undergo any possible degradation of their brain, officially called phantasmal pattern depletion, known colloquially as Zombie Syndrome.
Ghosts cannot do much. Their very presence causes certain computer functions to malfunction, they are not always capable of speech, and writing is well beyond their grasp. Moving more than ten miles beyond their crystals is impossible. Electrical currents, when channeled correctly, can trap them entirely, and there are a number of spells designed specifically for dispelling ghosts. They can, however, gesture quite easily, and gaze fondly or perhaps not so fondly on their family and friends.
The nature of the phantasmal form varies from person to person. One of the first things ghosts do is have the magician in question tailor their appearance. Most prefer a younger, more polished version of their original form, with a few phantasmal touches around the edges like a lack of legs or adding a gray tinge. A few go more extreme, usually as preparation for taking a work position. This will include such things as ragged clothing, chains, or a hood and black space rather than a head. The traditional ghost look, basically.
The exact nature of the spell is quite complicated, although not particularly difficult to have performed on oneself. Most avoid it, as ten years being a bodiless phantasm is a bit boring. As such, there has grown to be quite a job market for ghostly jobs. As it is difficult for ghosts to fully interact with the world, they are primarily found through agencies, and used for several different purposes. The most common is as spies, but only in a most general sense. Another popular choice is a contract to haunt a specific area in a building to add atmosphere or serve as a guide for a quest or a guard for an important object.
Not many people use the spell, as there is some confusion about what exactly a ghost is. Some theorize they are the soul of the deceased person, imprinted on a crystal and lingering in this world. Others insist it is merely a shadow of the person, a transcription of their thoughts and memories, and that the real person has already moved on. They are afforded limited legal rights, and any money they earn through employment is submitted to the descendant of their choosing. Advocacy groups generally agree that this cause is not worth their time pursuing since ghosts already had time alive as a citizen with rights, and since the extension of their time here is of a questionable nature and decidedly non-permanent nature.