Story
Most episodes are self-contained short stories in which the series narrates the suffering of a different individual caused by one or more antagonists. A website known as "Hell Correspondence" (Jigoku Tsūshin, "Hell Correspondence"?) may only be accessed at midnight by one who harbors a desire for revenge against their tormentor. Should someone submit the name of someone against whom they have a grudge, the Jigoku Shōjo (Hell Girl) will offer them a straw doll with a red string wound about its neck. If the string is pulled, she will ferry the target of the revenge straightaway to Hell, however the client agrees to a pact where those who request her intervention will also be sent to hell at the end of their natural lives.

During each story, the protagonists' dramas are explained in detail from the start of their grudges, through the escalation of their torment until it becomes unbearable and they resort to accessing the Hell Correspondence website. The contents of the site are only a text: "あなたの怨み、晴らします。" (which is read "anata no urami, harashimasu" and means "We will take revenge, on your behalf."), a text box where the grudge's object must be written, and a "送信" (Send) button. Some time after the post, they are visited by Enma Ai, a young red-eyed girl wearing a traditional sailor school uniform (usually the dark version used only in winter months). She hands them a straw doll, which is actually one of her assistants, with a red string tied to its neck. In the first season, the doll is always black, because it is always the same assistant, that is, Wanyūdō, but in the second season, the doll may also be red or dark blue, depending on which assistant it is (Hone-Onna or Ichimoku Ren, respectively). She then tells them that if they want their vengeance to be delivered, they must remove the string from the doll, and their enemies will be immediately taken to Hell. A black crest-shaped mark will appear on the protagonists' chests, which serves as a constant reminder that once their lives come to an end, they must give compensation for Ai's service by having their own souls also sent to Hell