It happens almost overnight. Everything is the same as it ever was and then suddenly, the earth is haunted by millions of ghosts. After the initial panic wears off, people in every country of the world welcome the ghosts into their homes, treating them like the long-dead relatives they believe them to be. They seem harmless, after all; why should anyone suspect that they’re not what they seem?
The more people believe in them, the stronger they get, and when they finally break through, nobody’s prepared.
Rank after rank of metal monsters march through the streets.