Mui is a supporting character in Undead Unluck, initially serving as the subordinate and assistant to Shen Xiang, a prominent martial artist and Union member. She is a young woman of Chinese descent with short brown hair, and she acts as Shen's secretary, handling logistics and support. Mui is kind-hearted and deeply caring toward her comrades, but her primary loyalty is to Shen, whom she is protective of and appears to harbor romantic feelings for. She respects him greatly and becomes angry or defensive when he is harmed.

Before awakening any supernatural abilities, Mui compensated for her lack of powers by training in martial arts to a level comparable to Shen's and by utilizing various ancient artifacts. Her most dramatic early act involves saving Shen after a fatal battle by using a powerful artifact to revive him as a jiangshi, a reanimated corpse, which preserved his martial skills but cost him his negation ability.

Following Shen's death, Mui inherits his former negation ability Untruth and becomes a member of the Round Table, taking the position of No. 2. Untruth allows her to force a target to move in the opposite direction of their intended action, as long as she is fond of the target and can see them. Later in the story, she gains a second negation ability, Unfade, which grants her immortality, making her the only character in the series to possess two separate negation abilities.

Mui's personal background includes the loss of her brother, which leaves her battling loneliness, but she remains strong and dedicated to protecting Shen and supporting the Union's cause. Her development sees her transition from a powerless aide to a formidable Negator in her own right, taking on greater responsibility within the organization. Her key relationships include her close bond with Shen and her growing camaraderie with other Union members.