Sent to an Asylum, I Had No Choice But to Create Gods

In a world where evil gods and the bizarre are quietly resurfacing during the Industrial Revolution, the protagonist is a librarian in a mental hospital, regarded by everyone as a cowardly madman. He obtains a blank "Book of Madness," discovering that by writing settings into it, he can "anchor" powerful fictional beings to reality, making them his loyal servants. From a gun-wielding detective to a dream-controlling sorcerer, and then to an unspeakable Great Old One, he silently builds a "Containment Facility" to fight against the apocalypse, becoming the only order in the darkness.