"Hell Girl" centers around a supernatural service accessible through a mysterious website that appears only at midnight. The site, known as the Hell Correspondence, allows individuals to submit the name of someone who has wronged them, summoning Ai Enma, the titular Hell Girl. Ai is a stoic, enigmatic figure who offers to send the target to hell in exchange for the petitioner’s soul. Once the contract is sealed with a red straw doll, the target is tormented by visions and ultimately dragged to hell by Ai and her companions—three straw dolls named Ichimoku Ren, Hone Onna, and Wanyūdū, who serve as her intermediaries.

The narrative unfolds in an episodic format, with each chapter or episode focusing on a new petitioner and their grievances. These stories explore themes of revenge, justice, and morality, often highlighting the darker aspects of human nature. Petitioners range from victims of bullying, betrayal, and abuse to individuals seeking retribution for perceived slights. While the immediate satisfaction of revenge is granted, the cost is steep: after death, the petitioner’s soul is condemned to hell, ensuring a cycle of suffering.

Ai Enma’s backstory is gradually revealed throughout the series, providing context for her role as the Hell Girl. She is bound to her duty as a result of a tragic past involving betrayal and a curse, which ties her to the supernatural realm. Her companions also have their own histories, adding depth to their roles as enforcers of the contracts. The series occasionally shifts focus to investigative journalist Hajime Shibata and his daughter Tsugumi, who become entangled in the mysteries surrounding the Hell Correspondence. Their efforts to uncover the truth about Ai and the consequences of the contracts provide a recurring narrative thread.

The tone of "Hell Girl" is dark and contemplative, with a strong emphasis on the moral ambiguity of revenge. The episodic structure allows for a wide range of human experiences and emotions to be explored, while the overarching narrative delves into the origins and implications of Ai’s existence. The series balances its supernatural elements with psychological and emotional depth, creating a compelling exploration of vengeance and its consequences.