Hell Girl is a very cute little girl from hell. She has servants who are spirits and she has a rather odd job. See there's a web site, and if you follow the instructions and do it at the right time Hell Girl will come to you. If you have someone you really, really hate she'll offer you a deal. She'll give you a little figure with a red string around it. If you still have hate in your heart just remove the string and then Hell Girl and her servants will remove that person to hell right now. The catch is, someday when you die you will also go to hell. So is it worth damning yourself for vengeance?
As you can guess the series is less about Hell Girl than the individual folks who petition her service. Since they are generally young folk I can only feel that they are damning themselves for practically nothing. I mean damning yourself to send a bully to hell? Truly karma is a bitch.
It's a beautifully animated anime, but in the end I find it rather empty and repetitive. Just remember to say no to hell people no matter how sweet the dream seems.