Jigoku Shoujo, translated and known as Hell Girl in English, is a series originally consisting of an anime which currently has three seasons. It has also been adapted later on into a manga series, a live-action television series which has finished airing, and a few games. As these adaptations follow different storylines, they are not canon to the anime series, though they have core similarities to the anime.
The story revolves around a girl named Ai Enma, who is better known as Jigoku Shoujo (Hell Girl). Her existence is known only by a small group of people, and most of these people know her for the service that she provides, which is to carry out grudges on behalf of the people who request her service by sending the person they hold a grudge against to hell.
The means of requesting her service has changed with time, with the latest means being a website known as the Jigoku Tsuushin (Hotline to Hell). This website is once again only known by a small group of people, often in the form of urban legend. It is only accessible exactly at midnight, and can usually only be seen by those who bear significantly powerful grudges. This website can be used to enter the name of the person they have a grudge against and send it.
After a request has been sent to Ai, she will usually investigate the client (the person who requested), and/or the would be victim. She often does this by supernatural means, and for various reasons, through which she decides whether to give her service or not to a client. She usually has her companions investigate the situation, and sometimes she joins in with them too. If she accepts the client's request, she will approach the client and hand them a straw doll. She will then explain the terms of her service, which is that if the client wishes to continue, he or she must pull the red string tied around the neck of the straw doll. After doing so, Ai will take the person who the client sent the name of immediately to hell. However, by pulling the red string, the client agrees to the condition of her service, which states that he or she will also be sent to hell, but only after his or her natural life comes to an end.
The story of the series has a recurring theme of injustice, hatred, suffering, and revenge. Elements like violence, harsh language, trickery, blackmail, animal cruelty, torture, insanity and such are found from time to time.