Ai Emna

The primary protagonist of the series, who is arguably an anti-heroine as well. With long, straight black hair and ruby-red eyes and pale skin, she is a spiritual entity with a tragic past, who lives in a place frozen in time as it basks in eternal sunset, along with her grandmother. Through an old computer inside their house, Ai is able to receive the names the clients have typed on the website, and she delivers this revenge.

She normally wears a black seifuku, or sailor uniform, but always wears a kimono with floral (or egg) designs when delivering the vengeance of a client. Ai started her career as the Hell Girl by her own act of vengeance on the villagers who sentenced her to a sacrificial death as part of their village's tradition. Her eyes, once a deep brown, turned red arguably at the point where Sentarou (her childhood friend and cousin who gave in under the villagers' pressure to bury her alive) gave the first shovel of soil onto her face. She broke out of her grave after a while, and took revenge on the entire village with her wrath, burning it to the ground.

Her task of fulfilling other people's vengeance and ferrying people to Hell is her punishment, a task which she had performed for 400 years after that incident. The Lord of Hell who gave her new life to exact others' grievances, made a pact with her; in exchange for her immortal form, she cannot enter hell and must remain on the shores of Hell, acting as the deliverer of people's hatred and vengeance. In order to serve these tasks, the Lord of Hell demanded that Ai forget her own hatred, numbing herself to the sufferings of others and becoming a mere observer of any happenings. If she hadn't this punishment, the souls of her beloved ones would have forever wander in hell, lost for eternity. Having no other choice, Ai agreed with the Lord of Hell and became the Hell Girl.

Although this task is presented as atonement, it is unknown whether she will ever be freed of it. Wanyūdō noted she still had feelings, though, although she did not express them strongly, and it was later revealed that Ai had been ordered to close her heart by the Spider. But the experiences she has with the Shibatas reawakened her discontent with her terrible fate and later apparently reawakened other emotions, or at least Ai's ability to express them. When enraged, Ai demonstrates the ability to hurl great blasts of energy, as well as the power to create elaborate illusions and teleport. She also has the ability to show someone the future of a grudge, as she showed Yuzuki in Episode 18 of Mitsuganae.

In the second season, Ai becomes more expressive and shows more emotions, being more willing to interact with her "clients" and victims. She even puts up a "V for Victory" sign in front of her target by way of mocking him as he is dragged to his doom. She had also been seen reading from a fashion magazine while her compatriots watch over their client, and had showed concern towards a mother who willingly ended her life so that her daughter doesn't have to send her to Hell. As she witnesses Takuma Kurebayashi's disheartening persecution, Ai recollects her emotions pertaining to her own wrongful persecution and she defies her 'employer', the Lord of Hell, and becomes restored to human life, and killed shortly thereafter, when saving Takuma from his tormentors. After Ai's self-sacrifice, her body dissolves into sakura petals and drifts into the sky.

In the third season, Ai return to the series after. In the beginning of the season, she transports another girl, Yuzuki, to a strange illusion and dream state, where Ai possessed her. Eventually, her body is later released during The Six-script Lantern ceremony in her town in which the gate to hell is temporarily open allowing Ai to be released from her body. Ai eventually reveals to Yuzuki that she is destined to become her successor.
It is ironic that Ai's name actually translates as: Ai (love) and Enma (the Judge of the Underworld). A second translation of Ai, however, is accomplice, denoting Ai's role as Enma's assistant. Another meaning of her name is the kanji for 'sorrow'. Because her first name is never written in kanji, its meaning remains ambiguous.