From fattwiki

People naturally pay their respects to the dead. The person had, after all, just accomplished the personal, profound feat of dying.

– Haruki Murakami, 1Q84 (quoted in Dungeon World playbook)

A ghost is a spectral remnant of a being that was once alive. This may be a result of an undead being with the curse of Nacre being killed and coming back in its third phase of life. A ghost may also be a spirit left in the world from a time of great calamity, when a massive number of deaths kept Tristero busy.

Lacking physical form, ghosts are difficult to fight off without magical means or weapons of Ordennan steel.