"Detroit Metal City" centers on Soichi Negishi, a mild-mannered young man with a passion for Swedish pop music and a dream of becoming a successful indie artist. Despite his gentle demeanor and refined tastes, Negishi finds himself thrust into the world of death metal as the lead vocalist and guitarist of the fictional band Detroit Metal City (DMC). Under the stage name Johannes Krauser II, Negishi adopts a grotesque, demonic persona to embody the band's extreme image, which contrasts sharply with his true personality.

The series explores the duality of Negishi's life as he struggles to reconcile his personal identity with his over-the-top stage persona. While DMC gains immense popularity for its aggressive music, outrageous performances, and satanic themes, Negishi is deeply embarrassed by the band's vulgarity and the absurdity of his alter ego. His attempts to distance himself from DMC are constantly thwarted by the band's ambitious manager, Terumichi Nishida, who pushes Negishi to embrace the Krauser persona for the sake of fame and success.

Negishi's interactions with other characters further complicate his situation. His unrequited crush on Aikawa, a sophisticated woman who despises DMC's music, forces him to keep his involvement with the band a secret. Meanwhile, DMC's rivalry with the flamboyant death metal band Jack Ill Dark adds to the chaos, as Negishi is pressured to outdo his competitors in increasingly ridiculous and over-the-top ways. The series also introduces a variety of eccentric characters, including DMC's devoted fans, who idolize Krauser II without knowing the man behind the mask.

Throughout the narrative, "Detroit Metal City" balances absurd humor with moments of introspection, highlighting the tension between artistic integrity and commercial success. Negishi's internal conflict—his desire to pursue his own musical aspirations while being trapped in a world he finds distasteful—drives much of the story. The series satirizes the music industry, fan culture, and the extremes of performance art, using exaggerated scenarios to underscore the absurdity of its characters' lives. Despite its comedic tone, the manga occasionally delves into themes of identity, self-expression, and the sacrifices required to achieve one's dreams.