Yang acts as assistant and companion to Mion, an Observer within the Program. Her designated role is Regulator, limiting her interventions to situations demanding higher-level authorization—such as eliminating participants who break rules.

She possesses medium-length dark brown hair secured with four bun covers and favors a sleeveless red qipao reflecting a Chinese aesthetic. A watch adorns her right arm, and her eyes remain perpetually closed due to the nature of her ability.

Her typical demeanor is submissive and accommodating, embodying her role as a loyal assistant. Yang rarely voices her true feelings unless compelled. This restraint stems from her Regulator responsibilities, often forcing her into passivity despite major events.

During the Program's initiation, Yang informs participants of the rules and announces the first format: 1-on-1 battles preceded by a 20-hour preparation period. In the Fourth Program, she receives authorization to deploy her ability against Leonhart after he violates a core rule by killing a participant outside his team, leading to his loss of Observer status.

Yang's ability, Millennium Eye, accelerates time by a thousand years for anything within her direct line of sight, effectively erasing targets from existence. Using this power exhausts her significantly. Keeping her eyes closed at all times prevents accidental activation.