In the fictional future city of Lancheng, young spirit controller Ye Qinghan unexpectedly contracts a black symbiotic spirit named Lin Ye, who was judged to be of low grade. Facing training, evaluations, and urban crises, the two go from mutual distrust to side-by-side cooperation. In the process of protecting companions and completing safety missions, they continuously grow, gradually discovering the true value of each other's abilities, and join hands to thwart the mysterious organization's plan to disrupt city order, becoming mutually trusted partners.