The Code:05; she's hailed as one of the most powerful Code:Breakers. At first, Sakura thought she was a man, but she is actually a woman. Rui acts very much like a tomboy but is truthfully immensely shy. She is one of the few to know Shibuya's true identity and often uses this secret to blackmail him. Her addition to the Code of Hammurabi is "and the punishment of death for evil".

Rui's ability allows her to manipulate her shadow to defend or to attack by slicing others shadows (the damage done to the shadow becomes real). Her most powerful technique is "Empress Paradox", a shadow monster which envelops her body and can even eats up Rui herself. When Rui loses her power, she becomes a mermaid.

She does not get along well with Heike in particular, as in the past she was a Re:Code under the command of "The Seeking One". Her reason for leaving them was because "the thing she needed to protect wasn't there"; this is later revealed as a request from "The Seeking One" to protect Ogami should Eden come after him in the event the Code:Emperor's soul in his left arm awaken. She was closest to Kouji and Yukihina, and once even took a picture together with them. Even though now she refers to "The Seeking One" as a monster, she still has deep respect for him.

Further revelations show that Rui belongs to a family of four, all of them (Rui, her parents, and her little brother) being power users. For this reason, her parents were murdered and the incident was covered up as an accident. Rui believed her brother was also dead, until the Code:Emperor showed her that he couldn't summon her brother's soul from hell, which meant he was still alive. Later, it turned out that her brother is the Code:Closer, Saechika.