Jigoku Shoujo, known as Hell Girl in English, is an anime series currently consisting of three seasons. It has also been adapted later on into a manga series which is still ongoing, a live-action television series which has finished airing with a total of 12 episodes, and a few games and mini-games. These adaptations are not canon to the anime series and follow different storylines instead, though with core similarities to the anime.
The story of the anime (and in fact the whole series) has a recurring theme of injustice, hatred, suffering, and revenge. Elements like violence, harsh language, trickery, blackmail, animal cruelty, torture, insanity, twisted and complex human emotions, and such are found from time to time. Therefore, the anime is not suitable for younger audiences and viewers, and is rated R-17+.
The story revolves around a girl named Ai Enma. Her existence is known only by a small group of people, and most of these people know her instead by the name Jigoku Shoujo (Hell Girl). Something of which the existence is known of just as much would be the service that she is rumored to provide, which is also far from common knowledge. It is this service for which she is known as Jigoku Shoujo.
Ai's service consists of carrying out grudges on the behalf of the people who request her service. 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. There is very little content on the website, and it consists of only a message, a text box, and a 'send' button. If one is to receive Ai's service, they have to enter the name of the person they have a grudge against in the text box, 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, which is actually one of her companions transformed. She will then explain the terms of her service, which state 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.