Sonia Summers, a young investigator, has been relocated to the outskirts of the port of Libra after causing a commotion with her superiors. Libra is divided into two sections: "the Upper," which is the center of money and politics, and "the Outside." The Outside is rife with crime, corruption, and strange encounters with monstrosities called youkai. Each case Sonia works on appears to entail the participation of these enigmatic animals. Sonia meets three strange humanoid youkai — Bem, Bela, and Belo — who wish to defend humanity and combat the wicked youkai that terrorize them. They are rejected and harmed by humans when they show their actual forms while living as "Youkai-Ningen." They are shunned by other youkai for their human-like lifestyles, and they are rejected and hurt by other youkai for their human-like lifestyles.