Why I haven't written about this series yet is beyond me. Hell Girl is pure genius, and the source of my avatar: Ai's Eye.
Hell Girl (Jigoku Shoujo) is a series about a series of people who are wronged by other people, so they call upon the Hell Girl to take revenge on their behalf. She offers her caller a deal: She will send their tormentors straight to Hell, but when they die, their souls will also belong to Hell. "But... not until you die, of course." A black "seal of the covenant" attaches to the caller's body until their lives end.
This is the concept, but the further you get into the series, the more it focuses on reoccurring characters. Ai Enma is a girl from ages past, during a time in Japanese history when superstition and the will of the gods ruled over every aspect of human life. Without revealing too much detail, Ai was killed and took vengeance from beyond the grave. Her punishment is to carry out the deeds of a mysterious demonic entity, likely the devil. So she ferries souls to Hell for all eternity, and she's been carrying out this job for ages. All you have to do is type the name of your tormentor on a webpage at midnight. The page will only appear to those who desire vengeance.
This series is anything but shallow. A reporter named Hajime Shibata and his daughter Sigumi soon become involved in Ai's work when his daughter receives mysterious visions from Ai. Why she sees these visions, I'll leave for you to discover. As Hajime tries harder and harder to intercept Ai's work, his young daughter argues with him more and more over it, as the two become divided when it comes to the morality of vengeance. It dives into the subject on a deeper level that really makes you think.
Ai Enma's name is a play on words. "Ai" means "love" in Japanese, and "Enma", in Japanese mythology, is the judge who weighs your sin and determines whether you go to Heaven or Hell upon death. In this series, however, Ai Enma only carries out the task. Whether or not a person is to be sent to Hell is entirely up to the person who makes the deal.
If you like to get your story on, or you admire artistic imagery in anime, or you like art that brings good and evil into question, or if you simply like to watch bad people get punished, this series will likely be to your liking. If you come into it to watch it for one reason, you'll end up coming back for another reason. I first started this series in a phase where I was all about vengeance, but by the end of the series I cared more about the story and the characters than anything.
An eye for an Ai.