"The Devil Is a Part-Timer! High School!" is a spin-off manga series that reimagines the characters and premise of the original "The Devil Is a Part-Timer!" in a high school setting. The story centers on Sadao Maou, the former Demon King, who now lives as an ordinary high school student in modern-day Japan. Stripped of his demonic powers, Sadao navigates the challenges of teenage life while trying to maintain his identity as the once-feared ruler of Ente Isla. Alongside him is Emi Yusa, his former nemesis and the Hero who defeated him in their previous world. Emi, now a classmate, continues to harbor a deep-seated grudge against Sadao, though their dynamic shifts as they are forced to coexist in this new environment.

The narrative explores the comedic and slice-of-life aspects of Sadao's attempts to adapt to high school life, often juxtaposed with his lingering pride and memories of his demonic past. Supporting characters include Chiho Sasaki, a cheerful and kind-hearted classmate who develops feelings for Sadao, and Shirō Ashiya, Sadao's loyal demon general, who now serves as his overprotective and overly dramatic best friend. The series incorporates lighthearted humor, school-based antics, and occasional nods to the original story's fantasy elements, though the focus remains on the characters' interactions and personal growth within the high school setting.

Themes of identity, redemption, and the clash between past and present are woven into the story, as Sadao and Emi grapple with their shared history while trying to forge new paths in their human lives. The manga balances comedic moments with character-driven storytelling, offering a fresh take on the beloved characters from the original series while maintaining a standalone narrative accessible to both new and returning readers.