The plot of the series revolves around three youkai, Bem, Bera and Barro, who arrive at a large coastal city and come across an evil atmosphere, which was brought about by immoral behavior by humans and mischief caused by monsters and youkai. They therefore decide to stay in the city, fighting against other monsters and yōkai which attack humans, making a few friends in the way. Even though the three youkai are often abused by other human beings due to their appearance, they still strive in protecting the human populace of the city from other monsters, one day hoping to become human beings in return for their good actions.

Bem, Bela, and Belo are not "monsters," nor "humans," but "humanoid monsters." They usually disguise themselves as a human family living together, but their appearances transform into ugly monsters when their emotions become uncontrollable due to intense anger or extreme sorrow. Even if they save humans out of a sense of justice, they are feared and hated by humans just because they are humanoid monsters. They have lived in this manner for centuries, and their only wish is to become humans as soon as possible. One night, Bem saves a man, and becomes friends with detective Natsume. At Natsume's house, he finds a photo of a man who may hold a clue as to how to become humans. They go to meet the man, Ogata, who denies any knowledge and disappoints them. Meanwhile, the case of the man Bem had saved, rapidly unfolds, and Natsume finds himself in trouble. Can Bem save Natsume?! Will Bem and his sidekicks' dream come true?!

The plot of the series revolves around three yokai (supernatural creatures), Bem, Bela and Belo, who arrive at a large coastal city and come across an evil atmosphere, which was brought about by immoral behavior by humans and mischief caused by monsters and yokai. They therefore decide to stay in the city, fighting against other monsters and yokai which attack humans, making a few friends along the way. Even though the three yokai are often abused and discriminated against by other human beings due to their appearance, they still strive in protecting the human populace of the city from other monsters, one day hoping to become human beings in return for their good actions.

Bem, Bela and Belo arrive at a new town plagued by a series of mysterious, unsolved cases which, as they discover, are caused by another youkai, one more powerful than they have ever encountered. The story will also focus on Belo's first love, and his increasing desire to become human. In the meantime, Bem and Bela have found a way to become human, but are conflicted about whether to let just Belo turn human, or along with Belo, become humans themselves.

For 1982 a 26-episode TV series sequel to Youkai Ningen Bem was planned. Because the original producers disbanded, the animation was done by Topcraft. 2 episodes were created and the project shut down without airing on television. The episodes were released to the public on a LD-Box Set a decade later. 2,000 units were printed and all were sold out.