Ai Enma is the main protagonist of the series, and is the one known as the "Jigoku Shoujo", referred to in the English version as "Hell Girl". As such, she makes a regular appearance in the series, although her appearance is smaller and less frequent in "Jigoku Shoujo Mitsuganae". She is played by Sayuri Iwata in the live-action television series.
Due to the nature of the duties which she is required to carry out, Ai can also be claimed to be the anti-heroine of the series. She also almost never exposes signs of being moralistic or idealistic, and occasionally opposes even those who are attempting to stop her for a good cause.
Ai has long, straight black hair in a hime cut that she keeps untied. Her skin is significantly pale, and she possesses red eyes, although they were originally brown before she was buried alive. Ai also has light pink lips. She maintains a thirteen-year old girl physical appearance, and has remained as such for well over four-hundred years.
Her usual attire consists of a dominantly black seifuku, similar to Japanese school uniform, with some parts colored white and red. However, while performing the act of taking someone to Hell, Ai always wears a kimono instead, which is dominantly black, with either temari, which are hand-woven thread balls, or floral design. Both patterns alternate back and forth through the series.
Ai wears a mask of cold personality. Even in situations in which are emotion-evoking, she doesn't appear moved in the least. Additionally, Ai is oddly silent and serious. She seems to only chat when the need arises, rarely speaking simply for the sake of it. In the event that Ai does talk out of ordinary circumstances, it is about something in which she believes is necessary for someone to know, or to correct somebody where needed. The main reason for her introverted personality is suspected to be a result of her having grown used to silence.
As the series goes on, Ai does become slightly more expressive, and a tad less cold, serious, and silent. However, the difference is extremely minor. Interactions from her side are a little more varied, and less grim later on, especially toward her clients and victims. In some scenarios, Ai actually goes to the lengths of mocking clients a bit like her servants before sending them to Hell. She has also increased her attention and shown concern towards the more innocent clients and victims. An example of this would include the time when she reassured a lady who was requesting her to have Ren, one of Ai's companions, watch over her daughter after she willingly ended her life so that her daughter didn't have to be sent to Hell.
It is later implied by Wanyuudou that Ai still has her feelings, but just chooses not to express them much. It is revealed later on that she had been ordered to close off her emotions by the Master of Hell. However, in rare, but possible, instances, Ai has defied that order and used her emotions to guide her actions, as opposed to only following the duties given to her. The first of such series of occurrences is near the end of the first season, when she enhances through her actions the extent to which Sentarou Shibata's actions had hurt her. In trying to take revenge on Sentarou's living descendants - Tsugumi Shibata and Hajime Shibata, Ai's true hatred comes forth. She urges Tsugumi in many forms to make her send her father, Hajime, to Hell, although her attempts were deemed unsuccessful. She also burns down the temple which Sentarou had built while shedding tears, which is a sign of bearing strong emotions, although it is unclear what Ai's motives behind her performance may have been. One such time in which Ai is noted to be able to have feelings, but not express or act on them, is when Hone Onna mentioned that when Ai was being forced to send an innocent person to hell on a certain day due to her duties, she was silently screaming in her heart for having to do it.
More than 400 years ago, Ai Enma was a human girl living in a remote village near the mountains. She was frequently bullied by other kids for her strange personality, and only had her cousin, Sentarou as a friend. At the age of seven, Ai was selected to be the sacrifice for the Seven Sendings, a rite where a seven year old girl was sacrificed to the Mountain God so that the village is given a good harvest. However, her parents secretly asked Sentarou to care for her as she lived in the mountains. Thanks to her parents, Ai managed to survive, hiding out in a waterfall known as Mutsumi Ridge where only Sentarou would visit her to bring her food and change of clothes. This would go on for three years. During this time, Ai and Sentarou's relationship developed and both of them became romantically attracted to one another, although not admitting so. Meanwhile, the village was going through a famine as the crops were dying out. One night, Ai was discovered when a group of boys followed Sentarou into the mountains. She tried to escape but was captured and violently brought back to the village. Ai and her parents were captured, blindfolded, and tied up . The priest gave them their rites before they were hit by a shovel and thrown into a deep hole to be sacrificed. The villagers forced Sentarou to be the first one to shovel ground to the hole to atone for his sins. While Sentarou began to cave in to their demands,Ai begs for Sentarou's help, and manages to shake part of her blindfold enough to see with one eye. What she saw however shook her to her very core. Shoveling dirt onto her and her parents' grave was none other than Sentarou himself. Sentarou's betrayal brought forth an immense hatred. As the villagers bury her, she vows to hate them forever even if she dies.
A short time after the incident, Ai escaped from the grave and exacts her revenge by burning the entire village to the ground in her wrath. She attracts the attention of the Master of Hell, who makes contact with her. He reveals that the souls of Ai's parents were being held hostage and makes a pact with her: in exchange for her parents not being sent to Hell, Ai must act as the messenger of people's hatred and vengeance. In order to serve these tasks, the Master of Hell demands that Ai forget her own hatred, numbing herself to the sufferings of others, and become a mere observer of any happenings. If she didn't accept this punishment, the souls of her parents would have to forever wander in Hell, lost for eternity. Having no other choice, Ai is then appointed as the Hell Girl.
Through the centuries, Ai travels around Japan becoming the messenger of vengeance to those with a strong hatred in their hearts. It starts when a client makes contact with her. Ai explains her services to a client, who has someone they hate and will be the recipient of the vengeance. She will give them a straw doll with a red string tied to it's neck. If he or she wishes to take revenge, the client may pull the red string. However, Ai always warns her clients that a mark will appear on them and their souls will also go to Hell when they die. If the client pulls the string, Ai puts on her kimono and goes to work. She shows the recipients a series of illusions, usually relating to their sins, and then sends them away as she ends them away in a dialog. As she does this, patterns of her kimono appear to come forth. Ai will then ferry that person's soul to Hell.
She teleports back and forth between the human world and an alternate dimension known as the Realm Of Eternal Twilight, where a house exists as her base of operations. The house is inhabited by her and her grandmother Sometimes, the Master of Hell will check in on her in the guise of a spider.
As time passes, so did the method of contacting Ai. The earliest known method was the Jigoku Ema, a stone in which the recipient's name is written and then put in the chest. In the early 20th century, Ai used a blank newspaper ad to advertise her services. With the arrival of modern technology, Ai would use the most well-known method of contact in the series: the Jigoku Tsuushin, a website where the recipient's name can be written. Whatever the methods, they share a similarity in that they are only effective at midnight and will only work for those who have a strong hatred in them. However, this means that the recipient's actual guilt in the matter is not a factor so long as the client hates him/her, and has led to innocent also people being sent to Hell.
While performing her duties, Ai recruited three beings as her companions. The first was Wanyuudou, the left wheel of a carriage that became a yokai. Ai encountered him when he tried to scare her. She convinced him to stop frightening people and he accompanied her as she met a client. After the mission, he decides to accompany her in her travels, becoming "her feet". The second companion is Ren Ichimoku, another yokai in the form of a katana. Ai meets him on the remains of a battlefield, stuck to the ground. He agrees to travel with her and Ai pulls him out of the ground. As she does this, Ren transforms into a human form. The third companion is Hone Onna, a former prostitute that was killed and dumped into a river. Ai met her as she unwillingly scared people in her skeleton form. Becoming her assistants, the three would act as investigators, monitoring a client's situation and investigating more about the client and/or the recipient if necessary.They hold great respect for their Mistress, and during their time together formed close relationships with each other and Ai, whom they care for deeply.
400 years have passed since Ai first became the Hell Girl. In that time, Ai has delivered the hatred of countless people. In doing so, she has succeeded in suppressing her own hatred and burying the painful memories of her past. Meanwhile, the Jigoku Tsuushin becomes a popular topic due to the quicker spread of information in the modern age, particularly amongst teenagers.
One day, Ai encounters Tsugumi Shibata on a train crossing. After the encounter, she estabilishes a telepathic link with Tsugumi, although she herself does not know why this happened. Whatever the reason, the link between them draws the attention of Tsugumi's father, Hajime Shibata. The link allows Tsugumi to see through Ai's eyes and identify the next client and/or the recipient of hate. Both of them would try to stop the revenge from being taken. Ai and her companions notice this, although she appears indifferent towards them, perhaps knowing they can't stop the cycle of hatred.
This changed however, when Ai received a client's request only to find it was a trap set by Jiru Du Ronfēru. During their confrontation, he uses his powers on her and manages to give her a glimpse of her forgotten past. Ai manages to send Jiru to Hell as the client pulled the string, but when she returns to the Realm, she sees Sentarou in the distance, indicating her past was beginning to resurface. She pieces back her memories and uses her link with Tsugumi to relay a message to Hajime. As both of them travel to Mutsumi Ridge, she maintains contact with Tsugumi as she realizes both of them have a connection to her past. She finally finds out the connection; Hajime is actually a descendant of Sentarou. This brought forth her hatred. She attacks Hajime and Tsugumi at the ridge. Her companions arrive and try to stop her, warning her acting on her emotions will send her to Hell. Consumed by hatred, Ai ignores their warnings and manages to hit Hajime and Tsugumi with her dark energy projectiles. Even after her companions tried to convince her not to do something like this, Ai Enma then proceeded to try to send Hajime and Tsugumi to hell. However, before she could do that, she was sent to hell herself.
Ai comes to at a ferry on the way to Hell, piloted by the Master of Hell himself. The Master of Hell tells her because of her actions, she will be damned to Hell. Ai refuses, saying she cannot go yet. The Master of Hell tries to stop her by shooting webbing at her, but she breaks through them and escapes. Meanwhile, Tsugumi and Hajime are teleported back to the temple. Ai sends Hajime away to the Realm while she sends Tsugumi back to their apartment and tries to convince her to take revenge on her father. Ai shows her the truth about her mother's death and Hajime's involvement in it. Hajime, Hone, and Ren arrive at the apartment. Her companions try to talk her out of her hate, but she knocks them unconscious. In a final attempt to make Tsugumi pull the string, she sends both of them to the scene of Ayumi's death. Her attempt proved to be unsuccessful, as Tsugumi loves her father dearly and refuses to take revenge. They return to the ridge where Ai reflects in her own memories. Tsugumi returns the Wanyuudou straw doll to her, saying she does not need it. Tsugumi states further that Sentarou loved her and regrets the actions he did back then, even building the temple as a sign of his remorse. The four of them (including Wanyuudou) teleport back to the temple. In a final release of her emotions, Ai destroys the Seven Child temple, the symbol of Sentarou's guilt, indicating she has forgiven him. Ai and her companions leave the temple, while Tsugumi and Hajime return home. As she had put aside her own hatred, Ai once again becomes worthy of the mantle of Hell Girl and continues to deliver souls to Hell.
In "Jigoku Shoujo Futakomori", Ai encountered Takuma Kurebayashi. He captured the attention of Ai because they both had a very similar fate. During episode 26, Ai showed empathy to Takuma because she knew that Takuma is innocent and had nothing to do with the accident related to his father. Ai decided not to bring Takuma in Hell. Suddenly, Kikuri was possessed by the Master of Hell and punished and made Ai a mortal for not fulfulling her task. Later on, Takuma saw Hotaru on the lake side. Because of that, he became angry and chose to take revenge for what he thought was Hotaru's death. He burned his own house down. Then, he was punished by the villagers for what he had done but Ai suddenly appeared and saved him. Unfortunately, when the villagers found out that Ai lost her powers and she became a mortal human, the villagers took revenge and they tried to kill Ai. Takuma shouted to stop hurting Ai. He swiftly went near Ai and he held Ai's hand. Ai said to Takuma that "It's all over".
- Ai has shown the ability to hurl large, deadly blasts of black-colored energy. This is first demonstrated when she meets face-to-face with the Shibatas, having remembered her past and hatred.
- She can teleport from one place to another. Throughout the series, Ai appears out of nowhere, therefore startling her clients.
- Able to take the lives away of her clients' tormentors, Ai can do so without necessarily making any physical contact to them, or damaging them physically. After terrorizing them with her illusions, she takes their lives away as the floral designs in her kimono wash over her victims. The victim appears to dissipate, afterward.
- Ai appears to be invulnerable to harm to some degree, as shown when Jiru Du Ronfēru telekinetic-ally hurls her around, and throws her against the walls, and later on, also sets her on fire, but Ai doesn't reveal any feelings of pain. However, this could easily be because Jiru was actually giving off illusions, and she instead has the ability to not be affected by illusions. This is further supported by the fact that when she got kicked in the stomach by Yuuna Serizawa, she was injured, and continued to feel the pain for a while after that. This, however, can be counter-argued that this could simply have been happening because she was using Yuzuki's body at the moment rather than her own.
- She seems to have the ability to possess others, but considering the fact that there has only been one case to argue this, it is difficult to say for sure whether it is her ability or not. The only event where Ai displayed this was when she was physically dead for some time and she possessed the body of Yuzuki Mikage in order to have a vessel to perform her duties as the "Hell Girl". Later on, after the Gate to Hell was opened for a while during the Six-Mon Lantern festival, she left Yuzuki's body, and retrieved control of her own physical body, as if she was resurrected.
- Ai is capable of creating large, intricate illusions, in which she often does to frighten her victims before taking them to Hell. She also creates illusions at other times, like when trying to convince Tsugumi Shibata to send her father to hell.
- At one point, Ai has displayed the ability to show someone the future of a grudge, as she showed Yuzuki Mikage, in Episode 16 of Mitsuganae. She also has the ability to show someone the past of a person, which Ai has performed on multiple occasions, first in the first season, and second in Futakomori. These abilities may be limited to some degree though, as Ai was unable to predict her confrontation with Jiru Du Ronfēru.
- Resurrection itself is an ability of Ai, as shown when she was buried by the villagers, and managed to rise from the dead to set her village on fire. Also, during the Six-Mon Lantern festival, she may have resurrected herself, though then the question would remain as to why she didn't revive herself until that point.
- Ai also has the power to create fire, which she has only used on two occasions. The first time it was shown, she burned her home village down to the ground with a wave of her hand. The other time, a similar ability was shown was when she created a ball of energy or fire, and used it to create a blast of fire to destroy the temple that Sentarou built. It seems that she creates fire, or perhaps she maintains the ability to create fire only when she gets emotionally-evoked, usually with anger.
- Ai was physically injured every season, once in Futakomori, and twice in Mitsuganae, and the first season each:
- In the first season, she was beaten up by the villagers of her village when she was alive.
- Later on, in the first season, she was thrown around through Jiru Du Ronfēru's telekinetic abilities in the episode Jigoku Shoujo versus Jigoku Shounen. However, she showed no sign of pain or resistance.
- In Futakomori, she was beaten to death again by some of the individuals of Lovely Hills.
- In Mitsuganae, she was kicked in the stomach in the episode My Teacher.
- Furthermore, in Mitsuganae, Ai was hit in the stomach with a dark bolt of energy fired by Yuzuki Mikage.
- Ai and Sentarou has been hinted to have had romantic feelings for each other multiple times.
- Ai has been shown to be able to play flutes, though their only use which happened before sending someone to Hell raises doubts as to whether it was just an illusion or not.
- Ai's kimono changes motifs every season. In season 1, it was a black kimono with large flower patterns. It is also shown as the first kimono Ai was given when she became the Hell Girl. In season 2, the kimono has flowery petals covering most of it, save in flashback scenes where Ai was still wearing her first kimono. In the final season, it carries pictures of fans and toy air balloons, the patterns of which appear to be moving.