Following the collapse of the Mechanical City and the near decimation of the Mohists, the fourth season unfolds with the Qin Empire striving for an era of peace and progress. The Emperor mobilizes a vast workforce to erect the Great Wall and implement advanced initiatives. An air of uncertainty shrouds the city as the enigmatic vessel 'Mirage' emerges on the horizon. In Shanghai, a coalition of rebels bands together to thwart the Emperor's grand designs. The Emperor marshals his forces, including the formidable Quicksand faction, the Yin-Yang School, the Net Trap Organization, and the skilled swordsman Shengqi, to quell the uprising led by the Mohists, Confucianists, and Taoists. Meanwhile, Tianming's journey of learning and growth persists as he grapples with escalating trials in his role as the Mohists' leader.