Mimiko Katsuragi is a human woman who works as a compromiser for the Order Coffin Company, the organization responsible for administering the Special Zone in Yokohama—a secret district where vampires reside following the destruction of Hong Kong during the Kowloon Shock. Orphaned at a young age, she was raised within the Company and later joined its Mediation department under the supervision of Jinnai Shogo. Despite being human, she chooses to live inside the Special Zone, driven by a genuine belief that vampires and humans are equal. She holds no prejudice against any race, and this open-mindedness defines her interactions with both red bloods and black bloods.

In the story, Mimiko is assigned to help the vampire Jiro Mochizuki and his younger brother Kotaro as they seek entry into the Special Zone. Her role as a mediator places her at the center of the tension between human authorities and vampire migrants. She develops a close bond with Jiro, often blushing in his presence and showing signs of romantic affection. During a critical battle against the Kowloon Children, she breaks Company taboo by willingly allowing Jiro to drink her blood when he desperately needs strength, an act that underscores her trust and devotion. Her motivations are rooted in a desire for peaceful coexistence and a sense of personal duty to protect those she cares about.

Personality-wise, Mimiko is kind, determined, and fair-minded, though she occasionally lacks cunning and can be somewhat naïve. She compensates with a natural charm and an ability to inspire trust in others, which makes her effective in her diplomatic work. Over the course of the series, she grows more independent and assertive, ultimately living and working alongside Jiro and Kotaro as a steadfast ally. While she possesses no supernatural abilities, her courage and humanitarian principles serve as her greatest strengths, allowing her to bridge the gap between humans and vampires in a world fraught with conflict.