Black Matrix Zero is set in the same fictional world as the original Black/Matrix game, though hundreds of years prior. Three divisions of humankind share the same world - white-winged people who are called angels, black-winged people who are called devils, and wingless people. Those who have wings have great powers and pay little mind to the wingless ones. The angels rule the world via a religious organization called the Prodevon Church, which ensures both the cooperation and ignorance of the wingless people. Source: Wikipedia, "Black Matrix (video game series)", available under the CC-BY-SA License.