"Drug-on" is a manga series that blends elements of science fiction, action, and psychological drama. The narrative centers around a world where humanity is plagued by a mysterious phenomenon known as "Drug-on," which causes individuals to transform into monstrous creatures driven by destructive impulses. These transformations are triggered by intense emotional stress or trauma, and the resulting creatures, also called Drug-ons, pose a significant threat to society.

The protagonist, Rindo Kazamatsuri, is a high school student who becomes entangled in the crisis when he encounters a Drug-on for the first time. During this encounter, he discovers that he possesses a unique ability to resist the transformation and retain his humanity. This ability draws the attention of a secretive organization known as the "Drug-on Control Bureau," which recruits Rindo to combat the Drug-on threat. The Bureau employs specialized agents who use advanced technology and weaponry to neutralize Drug-ons and protect civilians.

As Rindo delves deeper into his role, he uncovers the origins of the Drug-on phenomenon, which is linked to a series of unethical experiments conducted by a shadowy corporation. These experiments sought to enhance human capabilities but inadvertently unleashed the Drug-on curse. Rindo's journey is marked by his struggle to balance his duty to protect others with his own emotional vulnerabilities, which could potentially trigger his own transformation.

Key characters include Akira Tachibana, a skilled and stoic agent of the Bureau who becomes Rindo's mentor and ally; Yui Hoshino, a fellow student with a mysterious connection to the Drug-on phenomenon; and Dr. Kenzaki, a scientist whose research holds the key to understanding and potentially curing the Drug-on condition. The series explores themes of identity, the consequences of unchecked scientific ambition, and the resilience of the human spirit in the face of overwhelming adversity.

The plot is driven by a series of escalating conflicts as Rindo and his allies confront increasingly powerful Drug-ons while uncovering the truth behind the experiments. The narrative also delves into the personal histories of the characters, revealing how their past traumas and relationships shape their actions and motivations. As the story progresses, Rindo must confront the possibility that the line between humanity and monstrosity is far more blurred than he initially believed.