The Peaceful Lakeshore
A washed up writer decides to take revenge on a producer friend of his who became famous. During his attempted revenge the producer's wife is killed and their son is framed. The son contacts Hell Girl but decides not to go through with it. Shortly after this the producer is killed by the writer, but before the writer can kill the son a woman whose child he killed sends him to hell. This show is significant because it introduces character Takuma Kurebayashi, whom Ai empathizes with.
Aired 13/01/2007EP 14 - The Peaceful Lakeshore

Hell Girl: Two Mirrors
Ai Enma 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)