In Libra City, glory and corruption, prosperity and poverty all coexist. Sona is a young detective who tries to solve the many strange cases that occur in the city. During one such case, she meets Bem, Bela, and Belo. Able to transform into grotesque monsters, these three are referred to as “humanoid monsters.” Sony initially assumes they are the culprits, but they end up solving the case and helping the people involved. They do these good deeds in the hopes of one day becoming human.
Bem, Bela, and Belo stand against Dr. Recycle, a corrupt police force, the Unseen Council, who rules the city from the shadows, and the Unseen Council’s leader, another humanoid monster named Vega. Through a fierce battle that destroys the canal bridge, they manage to protect the city and thereafter vanish without a trace.

Two years later, Sonia is still trying to track down Bem, and a tip leads her to the pharmaceutical company Draco Chemicals. That’s where she meets Belm Eyesberg...