The Bound, also called Sin-Eaters, Fogmen, or Ghostwalkers, are humans near death who have been given a second chance at life by making a Bargain with ghosts known as geists. They are the protagonists of Geist: The Sin-Eaters.
Humans likely to become Bound are ones who have already been in contact with the dead in one way or another. They may be sensitive to spiritual activity, can hear or see ghosts, can foretell another's death, or any other number of ghostly contact. Most potential Bound have no clue as they became sensitive to the words and deeds of the dead; for some, it seems to be an innate talent, while for others it might be a chance supernatural encounter or pure and simple luck.
Whether they treat their "gifts" as a blessing or curse, their ability somehow communicate with the dead is part of what allows them to return to life. The other part is a deep desire to remain living, a desperate call for help that attracts a Geist to their situation. The Geist snares the soul before it is beyond their reach and offers it a life if the potential Bound will provide its body for the Geist's use. Accepting the offer, often called the Event or the Bargain, allows the soul to return, now with the added burden of the Geist in tow.
Sin-Eaters are often thought of as "possessed" by those with little knowledge of the true nature of the Bound. The actual existence the Bound shares with the Geist is usually more of a merger; the personalities, desires, and ideas of the two souls combine to form one being. Some Bound form more complete beings than others, working well with their new thoughts and desires, while others are tortured by the new voice whispering from behind their eyes.
Geists have no true physical presence in either the living or dead world, but many Bound choose to mentally give the Geist a separate identity and communicate with them as such. Others become extremely attuned to their Geist, able to piece together memories and ideas from their Geists on a more personal, primal level. The ability to communicate and co-exist with a Geist is known as Synergy; the higher the Synergy, the more the Geist and Bound act as one mind.
Most Bound return to the world of the living a changed person, needless to say. How they choose to spend their second chance at life is called an Archetype. One Bound might use their abilities to help other ghosts settle their business and transcend, while another might outright destroy ghosts causing problems. Some Bound will use their talents to improve themselves; others use them to improve their standard of living.
There is a subtle distinction between the correct use of the terms Bound and Sin-Eater. A Bound is any individual that is tied to a geist. A Sin-Eater is one that helps ghosts resolve their anchors and move on (in reference to the ancient practice of a person taking the sins of a deceased individual into himself so they can reach Heaven by symbolically eating bread over the corpse).
If a Bound drops to zero Synergy, they become Wretched. If a Bound loses their geist somehow, they become Vacant.
Abilities and Powers
The most obvious benefit to agreeing to the Bargain is the prospective Bound continues to live. However, having the power of a Geist at their fingertips allows the ability to call on Keys, a way that Bound can "unlock" the powers of the dead, Manifestations.
Sin-Eaters may also use Plasm, or ghostly residue, for a number of purposes. The most obvious is powering Manifestations, but Plasm also be used to heal, power Ceremonies, or open Avernian Gates into the Underworld.