After conflicting with her superiors, fresh-faced detective Sonia Summers is given a new assignment on the outskirts of Libra, a bustling port city that can be divided into two areas: "the Upper," where the wealthy and influential reside, and "the Outside," a place riddled with crime, corruption, and inexplicable incidents involving "youkai," monstrous creatures. Sonia soon discovers that each case she investigates is linked to these elusive beings. As she works, Sonia encounters three unique "youkai-ninjas" named Bem, Bela, and Belo, who are dedicated to safeguarding humans and opposing the nefarious youkai that terrorize them. These three individuals live as "youkai-humans," making them pariahs among other youkai creatures for their human ways. Furthermore, revealing their true forms leads to rejection and harm from ordinary humans. Despite the challenges they face, Bem, Bela, and Belo strive to coexist with humans while working to achieve their dreams of becoming human themselves one day.