Yun is a self-moving doll created roughly 400 years before the main events using Mujia technology by an individual named Che Yun, whose design she resembles. Sealed within a Tianshu scroll, she remains dormant until summoned by someone bearing the reincarnation of Che Yun's spirit. This occurs when Fu Yin discovers the Tianshu scroll, triggering Yun's release. Upon activation, Yun immediately demonstrates her technological capabilities by constructing magnetic prosthetic arms for Fu Yin's sister, Ning, who lost her original limbs years earlier. These prosthetics function through neural connection, restoring Ning's full mobility and combat capability.

Yun possesses the ability to transform between a humanoid form and a more powerful fox-shaped mechanized battle unit called "Yun-hu" (Cloud Fox), significantly enhancing her combat effectiveness against constructs of the Taibai Empire. Beyond direct combat, she functions as a guardian and power source linked to the Tianshu scroll and the Xuan Yuan Sword wielded by Fu Yin. Her connection to Fu Yin deepens with the revelation that he is the reincarnation of her creator, Che Yun, explaining his unique ability to unseal her.

Throughout the conflict, Yun participates in key battles alongside the resistance, fighting imperial forces and confronting the empire's massive construct superweapon, the Zhengtian. During the climactic battle, Yun sustains severe damage while fighting alongside Fu Yin and Ning. This critical damage impairs her functionality, resulting in a loss of power to the prosthetics she created for Ning, leaving Ning unable to move her artificial limbs. The extent of Yun's recovery or operational status after this damage is not detailed.