Port city "Libra".
Libra is composed of 3 sections: "Upper town" --- the center of politics, economy, and culture, where "the wealth" of the town concentrated; "Outside" --- a hotbed of crime and corruption, where people doubt each other and "Bridge" --- the only place connecting Upper town and Outside separated by a huge canal.
Libra is a town which as if represents the mankind's sense of discrimination by itself.

Sonia, a young female detective, who transfers to Outside from Upper town, investigates many mysterious cases and meets 3 ugly figures who fight to protect human being. She wonders, who on earth they are...

Three monster Youkai-Ningen are living secretly behind people's back, each having different thoughts in mind. Bem devotes himself to defeat evil for human being, wishing to become human himself someday. Bela is also attracted by human being and eager to become one, going to school and trying to understand what is human being. Belo, on the other hand, sees through human nature and the world, and gets absorbed in gaming.
All the more they interact with humans, they get hurt. Because of their ugly figure, they never get accepted by humans, even if they sacrifice themselves in the fight to protect human being...

Then there is a mysterious lady who is searching for those three Youkai-Ningen. She controls "a concealed assembly" which is dominating Libra in the back. What is the purpose of her conspiracy to capture Bem and the others?

Source: Official website

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Other: Youkai Ningen Bem
Prequel: Gekijouban Bem: Become Human