In the bustling Port Town of Libra City, a stark divide exists between the opulence of Upper Town, pulsating with power and wealth, and the lawless chaos of the Outside, plagued by crime and distrust. Sonia, a young and determined detective, relocates from the privileged Upper Town to the gritty Outside in pursuit of challenging cases. Here, amidst the societal disparity symbolized by a vast canal and a solitary bridge, she encounters three enigmatic creatures known as youkai ningen, or demon humans. Each harboring a unique blend of emotions and thoughts, these monstrous beings—BEM, seeking humanity for himself; Bela, yearning to understand and emulate humans; and Belo, immersing himself in the virtual realms of gaming—struggle to protect and connect with humanity despite their grotesque appearances. As they navigate a world rife with prejudice and conflict, their noble intentions clash with the harsh reality of human rejection. Meanwhile, a mysterious figure lurks in the shadows, orchestrating a hidden cabal that governs Libra City. Driven by unknown motives, she sets her sights on the trio, raising questions about her true objectives and the fates entwined with these extraordinary beings.