The movie reveals the events before Ge Nie and Tianming defeated 300 soldiers at Huangyang Chuan right at the start of season 1. The events will retell how Tianming and Ge Nie met. A new character and her relations to the Western Regions will be introduced as well.

Source: wuxiaedge.com

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Prequel: Qin Shi Mingyue: Bai Bu Fei Jian
Other: Qin Shi Mingyue: Luo Shengtang Xia