Four centuries in the past, Ai burns her village down in revenge for her own death. As the villagers burn to death, Ai approaches the shrine and the tree where she was buried, which are also burning, and breaks down crying. A voice asks is Ai is happy after her revenge and Ai looks up to see a bizarre-looking spider hanging from the shrine's gate. The spider brings her to the gate of Hell where she sees the souls of her parents imprisoned in the roots of the tree. The spider possesses the jellyfish floating over the gate and tells Ai that she must be punished for her vengeance. Ai says that she did nothing wrong, but the spider tells her that she will not enter Hell. Instead, she will remain in the world of the living to understand the sins she has committed. If she refuses, her parents will be sent to Hell. Ai then finds herself dressed in a flower-patterned kimono and standing near a boat as the spider's now-disembodied voice tells her that henceforth, she is to be known as Ai Enma, the Hell Girl.
In the present, Wanyuudo masquerades as a school groundskeeper. Some of the students greet him and they exchange lighthearted jokes. After they leave, Wanyuudo turns his attention to another student whose notebook and shoes have been defaced with insults. As a lab begins, she dons a lab coat, only to find that the sleeves have been riddled with pink staples while Ichimoku Ren watches from the ceiling and the student says that she's used to the bullying she's been receiving. The scene transitions to a flashback where Hone Onna says that the student doesn't know who to take revenge on. Ren says that she has been accessing the Hell Correspondence every night, entering and erasing the names of her classmates. Wanyuudo says that no requests have been submitted, but Ai has taken an interest. Ren suggests that they investigate. The scene transitions back to Wanyuudo observing the student from the grounds. The student opens her pencil case and is horrified when caterpillars spill out. While the rest of the class freaks out, the student uses her notebook to drop the caterpillars outside. The teacher appears and asks the class representative what happened before giving her itineraries for a class trip. The teacher, Ms. Kamishiro, asks the student, Maki Onda, to come with her. Ms. Kamishiro talks to Maki, who reveals that the bullying has been ongoing since the beginning of the year. Hone Onna listens in while disguised as a staff member. Later, Wanyuudo asks around and a couple of students tell him that Maki hasn't done anything to draw that kind of attention to herself. Wanyuudo asks the students why they haven't helped Maki and the students tell him it's not their problem. As the school day ends, Ms. Kamishiro tells Maki to let her know if something else happens. Maki asks Kamishiro if she'll really be helpful. Ren and Hone Onna walk in disguised as teachers and Ren comments that students don't trust teachers, calling Hone Onna "Ms. Sone". Hone Onna admonishes him, calling him "Mr. Ishimoto". Kamishiro says that she wishes she could do something for Maki. That night, Maki once again accesses the Hell Correspondence, but does not submit a name.
During lecture the next day, Maki receives text message saying that the sender knows who is behind the bullying that Maki is experiencing and telling her to come to the locker room during lunch. When Maki enters the locker room, the door closes behind her. Suspicious, Maki heads into the shower room and sees a figure in one of the shower stalls. When she opens the stall, however, the figure is revealed to be a mannequin with a wig and uniform added. The door slams shut and all of the showers turn on. Maki makes a break for the door only to find it locked. She calls for help, but eventually passes out from the heat and wakes up in the nurse's office. Ms. Kamishiro tells Maki that she came running as soon as she heard Maki's screams and then comments that they both have really soft hair. That evening, Wanyuudo finds Maki at the school garden and comments about how hardy the flowers are. Maki says that it's because the flowers have someone to watch over them. Wanyuudo asks if Maki can keep going and Maki says that she's fine now. That night, Maki bakes cookies for Ms. Kamishiro. The next day, Maki brings the cookies to school, but finds her shoes full of tacks. The class representative, Nakase, leads Maki to a storage room, where she shows Maki a terrarium full of caterpillars and says that she saw Ms. Kamishiro putting them into Maki's pencil case. Maki also finds the mannequin from the locker room, causing her to drop the cookies in fright. Nakase asks Maki not to say that she told her, but Maki runs out of the building and is seen by Kamishiro. That night, Maki enters Kamishiro's name into the Hell Correspondence. Ai appears behind Maki and brings her to the sunset world, where she gives Maki Hone Onna's straw doll. Ai states the terms of the deal and Maki demands to know why it's costing her her soul, saying that Kamishiro is the one in the wrong. Ai tells her to either accept the terms or return the doll. Maki almost returns the doll, but decides to think on it.
The next morning, Maki finds her locker stuffed with caterpillars. Kamishiro appears and drags Maki to the storage room, mocking Maki for trying to curse her. Kamishiro pockets the doll and mockers Maki for dropping the cookies. She then attacks Maki with a bottle of hydrochloric acid, saying that she bullies people as "experiments" for her own amusement. Kamishiro then threatens Maki with the bottle and demands that she help Kamishiro bully other students, starting with Nakase, who ratted her out. She also says that its fun to do things to others that you wouldn't want to have done to you. Maki manages to knock the bottle out of Kamishiro's hand, causing the acid to burn Kamishiro's face, and grab the doll. Maki pulls the thread and Kamishiro vanishes as Ai rides forth to claim her soul.
Kamishiro awakens in a spotlight and wonders where she is. Ai and her minions appear dressed in lab coats and Ai says that it's time to start an experiment. Kamishiro demands to know who they are and tries to walk over to them, but crashes into a barrier and falls over. It is then revealed that she is trapped in a flask connected to a giant chemistry apparatus. Wanyuudo says that Kamishiro seems to have a headache and Ren mockingly speculates that she's running out of oxygen. Hone Onna suggests creating some. Wanyuudo conjures up some manganese dioxide and Ren reacts it with hydrogen peroxide. Kamishiro demands to be let out, but collapses again. Hone Onna notes that they are actually using limestone while Ren says that he's using dilute hydrochloric acid, with both feigning ignorance. Wanyuudo says that they made carbon dioxide. Kamishiro demands to know why they're doing this and Ren hops down from the apparatus and says it's because it amuses them. Hone Onna echoes Kamishiro's sentiment about doing things to others that one wouldn't want done to themselves. Kamishiro begs the minions to let her out and the flask shatters, revealing Ai, who banishes her to Hell. Kamishiro awakens on Ai's boat and is swarmed by caterpillars that crawl out of her clothes, mouth and hair as she is ferried through Hell's gate.
Back in the world of the living, Maki looks at the mark on her chest and walks away as Ai and her minions look on. They head back to the sunset world as a girl watches them from the other side of the fence. Maki and Nakase finish putting together the field trip itineraries when Maki notices that Nakase's staples are pink, suggesting that she had some involvement with the bullying. A candle with Maki's name is lit.
This episode contains examples of:
- Adults Are Useless: Because sometimes they're the bullies.
- The Bully: Kamishiro, who tries to force Maki to do the same thing to others. The ending also implies that Nakase had a hand in bullying Maki as well.
- Bystander Syndrome: All of Maki's classmates notice her getting bullied but don't reach out and offer her any help. When Wanyuudou asks two female students whom he's befriended why they won't do something about it, their justification is that they're not that close to her. In the end, the only student that does help her is implied to have been a participant in bullying her as well.
- Foreshadowing: Mid-way through the episode, Nakase texts Maki to go to meet her in the showers to reveal to her whose been bullying her, however, when Maki goes there, Nakase isn't there and is instead subject to a cruel prank that Kamishiro "rescues" her from. While the mannequin used in the prank suggests that it was Kamishiro's doing, it's never explained why Nakase never showed up or even why directed her to the place where the prank would transpire in the first place. This hints that Nakase was complicit in Maki's bullying before the ending twist confirms it.
- Hypocrite: See Ironic Echo below. Kamishiro doesn't like having her own sentiments quoted back at her.
- Ironic Echo: Hone Onna quotes Kamishiro's sentiments about bullying right back at her."It's so fun to do things that you wouldn't want to have done to you."
- Ironic Hell: Kamishiro gets swarmed by the same caterpillars she used to bully others on her boat ride to Hell.
- It Amused Me: Kamishiro's entire motivation for bullying people, which gets thrown right back in her face by Ai's minions.
- Lab Coat Of Science And Medicine: Somewhat justified with Kamishiro, who is a science teacher and may have to work with harmful substances for lessons in subjects such as chemistry. It's then invoked by Ai and her minions during the Hell banishment, who dress up as a chemistry teacher and students respectively and perform a mock chemistry experiment.
- Louis Cypher: Hone Onna and Ichimoku Ren introduce themselves as "Ms. Sone" and "Mr. Ishimoto" respectively.
- Psycho Lesbian: Kamishiro, who has a sick fascination with Maki.
