Rei Myao is an unregistered Chinese individual in a future society dominated by pervasive surveillance, existing without official records or monitoring. This status allows operation beyond the system's reach. Rei frequently wears traditional Chinese dress and masters kenpo, wielding martial arts skills in combat. A strong affinity for cats is consistently evident in Rei's behavior and presentation. As the oldest member within the central group, Rei assists Hazuki Makino, Ayumi Kono, and Mio Tsuzuki following the attack on their friend Yuko Yabe, continuing prior efforts to protect girls targeted by a serial killer.

Functioning as a protective force, Rei provides physical security during the group's investigation into child murders and organ thefts. Collaboration with the hacker Mio Tsuzuki aids in exposing systemic corruption and bypassing surveillance infrastructure. Temporary blame falls on Rei for the murders of Yabe and Nakamura, though involvement centers on countering threats, not perpetrating them.

Rei Myao's unregistered status holds significant narrative weight, enabling actions outside legal frameworks and highlighting societal marginalization. This status directly facilitates the group's challenge to authority figures and evasion of pervasive monitoring systems during their pursuit of truth. Rei's combat expertise proves critical in confrontations against antagonists and security forces. The available materials detail no concrete backstory elements such as origin, family history, or specific life events before the film's events, nor information regarding Rei Myao's presence or development in other media beyond the original motion picture.