For the most part the episodes deal with a character who is being wronged by some other person. The first several episodes are pretty straight forward. Eventually, the need for revenge is more of a gray area, and at times the tables are turned. You need to give this one a few episodes to get going. At first I thought it would all the variations of the same morality play over and over, but four or five episodes in a story arc starts to form, particularly with the addition of a returning journalist who is trying to find out who Hell Girl is and what is going on.
It is an interesting story and does pose questions about morality and ethics that I do not typically find in anime. It is fairly dark at times, but not overly adult. There is nothing sexy going on, save the occasional, slight sexualization of Ai (Hell Girl) which is typical of anime. Occasional strong language, and the theme may not be well suited for younger viewers, but overall a nicely done show.