In a supernatural world where humans and demons coexist, in order to maintain the delicate peace of different races, high-level personnel from various countries have agreed to form law enforcement unions. Such unions are spread all over the world and carry out various matters, large and small. They are said to be awarded by the government, but they are just under the banner of respectability. In fact, they are independent organizations that accept tasks of different levels and receive corresponding rewards.
The story begins with the sudden appearance of the "Dark Union", and a little-known war broke out. In this war, Xin Jiuyan's (female protagonist) master Xin Tanhun was killed. In order to avenge his murder, Xin Jiuyan left the place where she stayed before and searched for traces of the Dark Union on the mainland...