From the introduction:
Broken World is designed to be run as a set of extraordinary and powerful characters overcoming ruination in a vast, multi-dimensional fantasy setting (by default, the setting of Kill Six Billion Demons). Each game is designed to follow the characters as they struggle with a broken world.
The core world of Kill Six Billion Demons is a multiverse - filled with hundreds of thousands of cultures and thousands of races, along with angels and devils. They all interact through the ruined and holy city of Throne, the hub-city at the center of all creation. Each world is a physical place that can be traveled to by means of a King’s Gate, which connects to the multiverse-spanning King’s Road. The road runs through each reality, and the Void Between Worlds, a great emptiness outside of creation.