A monster crosses over into... «We Are All Completely Fine»

A monster crosses over into the everyday world. The mortals struggle and show great courage, but it`s no use. The monster kills first the guilty, then the innocent, until finally one remains. The Last Boy, the Last Girl. There is a final battle. The Last One suffers great wounds, but in the final moment vanquishes the monster. Only later does he or she recognize that his is the monster`s final trick: the scars run deep, and the awareness of the truth grows like an infection. The Last One knows that the monster isn`t dead, only sent to the other side. There it waits until it can slip into the mundane world again. Perhaps next time it will be a knife-wielding madman, or a fanged beast, or some nameless tentacled thing. It`s the monster with a thousand faces. The details matter only to the next victims.
As for the Last Ones, the survivors of each spin of the wheel, the best they could hope for was to learn how to live with their knowledge.