Echo research, discovered in 9014 and based off of the ancient teachings of The Kingdom of Zeno, details and experiments on the connection between a person and their soul, as well as the power it can grant someone when certain conditions are met. Originally being nothing more than a stepping stone to other research, the Deep Void Incident of 14971, led to it officially becoming its own branch in 14974. It then shifted its focus onto the Echo Initiative, with the Numbers of Generation One being created in 14976, followed by Generation Two after the second Deep Void Incident, in 14989.
Echoes as we know them today are commonly thought to be the result of some kind of external influence from the Deep Void, changing the properties of a human's soul, and allowing them to develop incredibly powerful and diverse abilities ranging from Light Energy Manipulation to Time Travel. This claim has been disputed by some, but is generally accepted due to a lack of evidence on the contrary. The Echoes can over time develop their own personalities- Although the requirements for such a development are currently unknown, it has been theorized to have a direct correlation to the amount of power available to the user. The Numbers who have managed to live in harmony with their Echo personalities have had statistically significant increases in their power output.
Echoes have also been linked to Power Circles and the mythical creatures of Angels and Demons.