There is a rumor. There exists a message board called Jigoku Tsushin where one can access only at midnight. It is said that if one writes his grudge against someone, Jigoku Shoujo appears and she takes the person to the Hell.
[Source: AnimeNfo]
Enma Ai once again returns as the Jigoku Shoujo, who uses Jigoku Tsuushin (Hell Hotline) to allow people to post their grudges on their tormentors, sending them straight to Hell. In exchange, the users of the website will end up in Hell after they die. Meanwhile, a mysterious girl with blue eyes called Kikuri appears and seems to have strange intentions towards Ai and Jigoku Tsuushin's operation.
[Source: Anime News Network]
After Ai Enma's supposed death after the events of the 2nd season, her three helpers, Ichimoku Ren, Wanyuudou and Hone-Onna live out their lives in relative peace. This is suddenly shattered when Kikuri returns to recruit them. Meanwhile, Ai mysteriously reappears from the dead and uses the body of a young schoolgirl, Yuzuki Mikage, to continue the Jigoku Tsūshin operation. Yuzuki is aware of Ai's presence however, when she can see what Ai sees.
[Source: Anime News Network]
"Jigoku Tsushin," a website that only accessible exactly at midnight.
If you post a hopeless grudge there, Hell Girl will appear and drag your hated foe into Hell.
The rumor sounded like an urban myth, yet it spread among the young people and turned out to be true.
The girl's name is Ai Enma.
When she sympathizes with a client's grudge, she deems their foe a target, and sends the target to Hell as Hell Girl.
However, the legend does not speak of the contract with the Hell Girl.
Once you have your retribution, you will have to pay the price for it as well. Curses come home to roost. If you enter into the covenant, your soul will also go to Hell. That's only after you die, though.
And then one day, Michiru, a mysterious girl appears in front of Ai Enma.
Ai talks to Michiru, who doesn't remember who she is or why she is here.
Who the hell is she? Her secret past will be revealed!
[Source: Crunchyroll]