Messier Code or Messier Catalogue Number is a way of identifying Contractors, its name in the anime is derived from that of the astronomer Charles Messier. Ten years ago, during the time when the gates first came into being, the Stars were replaced by False Stars. This was the time when Contractors came into being. Each False Star has a corresponding Contractor, and they vibrate when their Contractor's power is being used. As such, Contractors are usually identified by their star. Accordingly, when a Contractor dies, their false star can be seen falling from the sky.