"BEM" is a supernatural action anime that revolves around three humanoid monsters known as "Bem," "Bela," and "Belo," who reside in the fictional city of Libra. Despite their monstrous appearances, they fight to protect humans from malevolent entities while striving to become human themselves. The series is set in a dystopian urban environment where corruption and inequality are rampant, with the wealthy elite residing in the upper levels of the city and the impoverished masses struggling in the slums below.

Bem, the leader of the trio, is a stoic and determined figure who wields immense strength and regenerative abilities. Bela, the only female member, possesses agility and a compassionate nature, often acting as the emotional anchor of the group. Belo, the youngest, is a mischievous yet loyal character with the ability to manipulate fire. Together, they confront various threats, including other monsters and corrupt human factions, while grappling with their own identities and the prejudice they face from society.

The narrative explores themes of redemption, identity, and the struggle for acceptance. Each episode delves into the trio's encounters with humans and monsters, often highlighting the moral complexities of their actions. The series also introduces Detective Sonia Summers, a human investigator who becomes entangled in their world, and Dr. Reijiro Yamaoka, a scientist with a mysterious connection to the monsters. As the story progresses, the trio uncovers secrets about their origins and the true nature of the city's corruption, leading to a climactic confrontation that challenges their resolve and purpose.

"BEM" blends action, mystery, and emotional depth, presenting a tale of outcasts striving to find their place in a world that fears and rejects them. The series balances episodic storytelling with an overarching plot, creating a cohesive narrative that explores the duality of humanity and monstrosity.