The story takes place in the second year of Emperor Guangde of the Tang Dynasty (AD 764), but there is a "hidden branch" in the historical line: During the Anshi Rebellion, An Lushan's son An Qingxu was not killed by Shi Siming. Instead, he led his remnants to retreat north to Youzhou (near today's Beijing) and established the "Dayan Continuation Regime" (historically known as the "Pseudo-Yan Remnants"). The natural dangers of Youzhou formed a "North-South Division" pattern with the Tang Dynasty. This regime has not been recorded in official history - because the Tang Dynasty later joined forces with the Uighur and Xi tribes to completely destroy the puppet Yan ten years later and destroyed all relevant historical materials, leaving only scattered cultural relics and folklore.
The world that the protagonist Zhang Yiwei travels through is precisely this "period of the Pseudo-Yan era that has been erased by history" (the fifth year since the establishment of the Pseudo-Yan regime). At this time, the internal conflicts between the imperial power (An Qingxu) and the military power (Gao Chengye, the descendant of the general Gao Shang) were sharp. Externally, they were squeezed by the Tang Dynasty, the Uighurs, and the Xi people. The people were undercurrents due to heavy taxes and strict control of cultural relics (the Pseudo-Yan royal family tried to strengthen the legitimacy of its rule by controlling antiquities).
