The anime's theme is about a site, which you can only access if you feel deep hatred inside your heart... In other words everyone can easily access this, and it even becomes a telephone app. (no, really, it does). This was never explained but it is assumed that each person can only use this site once. If you write the name of a person you hate on that site, you receive a Hell Doll. If you pull a string from the doll, the person whose name you wrote immediatly goes to a hell trial (supposedly you can avoid going to hell if you succeed in those trials. Throughout the series noone ever did.) which is pretty much the "ironic punishment" section before literally going to hell. After that, the site's user gets a tattoo, meaning he/she (usually a she) will also go to hell when they die (without their soul having a chance to go to heaven etc etc), though "when" they die isn't affected.
Each episode usually stands on its own, with the main protagonist of each series working and scooping around on the background, but otherwise remaining a minor character. The real protagonist is usually the site's user of each episode. We see him getting tortured by his harsh reality (oh and I DO mean harsh), how usually it's a specific person's fault (bullying, buckets of it) and how the protagonist decides that his/her soul is not worth it if his/her life is that miserable.
While in the first few episodes the anime does fool us that if your name is written on that site you're one sick psycho, as the episodes go on it starts becoming MUUUUUCH more complicated than that. People make mistakes, sometimes the people who they send to hell even protected them from worse things to come, sometimes it was just misunderstandings, sometimes it is the evil psychos who use the site and innocent people go to hell for no apparent reason. What you start believing is a mechanism for justice soon becomes muuuuch more complex and questionable. In addition the outcome isn't always what each episode's protagonist thought it would be.
As the series go on, you don't get used to it, it actually becomes worse. The Hell Girl herself (basicly hell's employee for commiting the "murders" and collecting the souls) has a phenomenally depressing backstory. Her helpers also share gruesome tails. And lastly the main protagonists... For the first season it's pretty sad. For the second season's protagonist story it is pretty darn depressing. For the third season it is "well here is the rope, you know what to do". Since (when I was 13-14) I made the mistake of watching all three series in a row, I actually went through depression for 1-2 months.
To sum it up, what I really liked about Hell Girl is that it actually promotes the value of human life, and therefore shows how big a dillema it is to actually kill somebody. Even better there is no fear of getting caught since the protagonists of each episode never have to actually interract with said "to-be-missing" person, so it's just a matter of conflicting ethics and emotions most of the time, as well as comparing the happiness your own soul MIGHT achieve one day compared to how miserable your current life is. If you want a good way to get depressed or some read food-for-thought, there you have it!
