Each episode typically follows the format of a self-contained short story where a person has been suffering torment from an acquaintance to the point that he or she accesses the Hell Correspondence website and submits a request to get rid of the person. Ai Enma, the Hell Girl, appears, and presents a doll with a red string on its neck that can send the named antagonist to Hell. When the string is pulled, Enma and her companions then torment the antagonist, offering a last chance to repent (which is usually refused), and ferries them to Hell. The price of the contract is that the person making the request will also have to go to Hell after his or her life is over.
Hell Girl (10 March 2018, at 04:08. UTC). In Wikipedia: The Free Encyclopedia. Retrieved from https://en.wikipedia.org/wiki/Hell_Girl
Song list of "Hell Girl"