Borrowed Life

Hidden within the modern city is an underground trading system known as the "Spirit Vessel Contract." Contract Masters, including the protagonist, have a special constitution that allows the dead to borrow their bodies for a time. Each transaction puts the Contract Master in danger: while the dead inhabit their body, their soul leaves it, leaving them vulnerable to being possessed by a living soul at any moment. In return, the dead must pay an "intangible price," which might be an obsession, an emotion, or a special ability from their life.