"The Demon Girl Next Door" centers on Yoshida Shamiko, a teenage girl who awakens one day to discover she has inherited demonic powers, including small horns and a tail. Her family, once a powerful demon clan, has fallen into poverty, and Shamiko is tasked with defeating a magical girl to restore their former glory. The magical girl in question is Momo Chiyoda, a stoic and powerful figure who lives nearby. Shamiko’s attempts to confront Momo are comically inept, as she lacks both the strength and the resolve to pose a real threat. Instead of becoming adversaries, the two develop an unlikely friendship, with Momo often assisting Shamiko in navigating her new powers and responsibilities.

The narrative explores Shamiko’s daily life as she balances her demonic duties with the challenges of being a high school student. Her interactions with Momo are central to the story, as Momo’s guidance helps Shamiko grow more confident and capable. Other characters include Shamiko’s mother, Sakura, who is supportive but often absent due to her job, and Anri Sado, a quirky classmate who becomes involved in Shamiko’s supernatural endeavors. The series blends slice-of-life elements with supernatural comedy, focusing on Shamiko’s growth as she learns to embrace her identity and form meaningful connections. The plot is driven by episodic adventures, often involving magical threats or personal challenges, while maintaining a lighthearted and humorous tone throughout.