Lucifers

Devils (also known as Lucifers) are malicious creatures with black wings, sprouting from their backs. They started to appear on the Ground a few years ago, attacking the people and invading the villages and towns. As a result, a new kind of bounty hunters has appeared, also known as Devil Sweepers, that were killing Devils for money. Lake Llandovery also was one of the Devil Sweepers, as he hunts them to find a cure for his frustrations.

It is revealed that the Devils (Lucifers) actually are Sera-Human infants, mutated due to DSHIS (Defective Sera-Human Infant Syndrome) - a genetic disease, that mostly affects Sera-Human infants, conceived in natural way (although, there's also a low risk of affecting adult Sera-Humans. In that case, it is called "tardive DSHIS").