Lou, whose full name is Zhenhua Lou, serves as the Kouran representative for the Red Dragon Expeditionary Group in Chaos Dragon. Originally an assassin for a religious organization in Kouran, she wields a sentient demonic sword known as Qisha Tianling, which she addresses as Lord or Your Highness. The blade can consume the souls of killers and possesses the personality of a young man; Lou keeps it sealed in a coffin between battles to prevent it from bewitching people. She has also bonded with a dragon eye, granting her additional power.

Her personality is cold, calculating, and enigmatic. She acts as a strategist and manipulator, often working behind the scenes to achieve her goals. Her motivations are driven by a deep-seated desire for vengeance, though the full nature of this grudge becomes clearer only as the story progresses. She is not motivated by power for its own sake but by a personal need to settle past wrongs.

In the narrative, Lou is a major antagonist whose machinations propel much of the conflict. Her role shifts from a seemingly loyal agent to a formidable adversary whose actions are consistently guided by logic and emotional conviction. Her relationship with her sentient sword is central to her identity, functioning almost as a partnership rather than mere tool use. Other significant relationships include her interactions with the main protagonist Ibuki and other members of the expedition, though these are largely adversarial.

Throughout the series, Lou undergoes little conventional growth; instead, the audience gains a deeper understanding of her origins and the traumas that shaped her. Her abilities include expert assassination techniques, combat proficiency with her demonic blade, and psychic manipulation powers that allow her to influence events and gather intelligence. She also demonstrates skill in espionage and information gathering. Her combination of martial prowess, supernatural weaponry, and strategic cunning makes her one of the most dangerous figures in the conflict.