At a hospital, a woman, Kyoko Kazama begins yelling at the staff, wanting justice for what they did to her daughter, Mika. She pulls out the black straw doll and is about to pull the string, when her husband stops her. Kyoko, however, has no idea it's her husband, but they leave. The superintendent's son, Iwa Senyudo, who is a doctor, explains to nurse Juri Honda that they shouldn't have left her daughter to die. In a flashback, Kyoko and her daughter Mika came to the hospital after surviving a car crash. Kyoko is fine on her own, but Mika goes into cardiac arrest and dies. Mika would've been saved if Iwa called another doctor, but Honda tells him to forget about Mika, and they don't save her. Iwa believes that Kyoko heard what they said that day and he fears that the truth will get out, but the nurse laughs it off, saying that Kyoko is suffering from amnesia, and she will forget about them. However, Honda knows what will happen if Kyoko pulls the string from the doll, and one of them will be sent to hell.
At the Kazama residence, Honda disguises herself as a maid and asks Mr. Kazama about Kyoko's condition. He says that Kyoko is at the point of forgetting what reality is, and she believes that Maki is still alive. The nurse searches the house for the straw doll and ends up stealing several 100 yen bills, claiming that Kyoko will forget about it. In Mika's room, Ai summons Wanyuudou, and he believes that Kyoko has forgotten about contacting them. Then, Kyoko comes to the room and sees Ai, mistaking her for Mika, and hugs her. Ai doesn't hesitate and stays with Kyoko for awhile, even cooking with her. Honda believes that Ai is only getting money out of Kyoko by playing as Mika, but Ai sees the evil in her. Hone Onna and Ren think that Ai is getting involved with Kyoko's life, but Hone Onna also thinks that Ai is getting tired of just ferrying people to hell.
Mr. Kazama returns that night, and Kyoko explains that their daughter returned and cooked for her. Mr. Kazama, however, thinks that Kyoko was having a hallucination and retires to bed. Kyoko looks through her journal and notices the words "Hell Correspondence" on one page. She types it on the computer, but gets nothing. The next day, Honda searches through Mika's room, but Kyoko is angered by this and orders her to leave. Ai then returns and comforts the poor woman. The two go out to the park, where Kyoko says that her amnesia keeps getting worse, and she could only remember when she looks through her journal. Ai takes pity on her, saying that she also goes through days of misery. Kyoko asks for her name and for a favor.
Ai poses as Mika in one of her dresses, much to the delight of Kyoko. However, she breaks down in tears, and Ai hugs her back. That night, Honda returns to the house and ransacks Mika's room, and finds the straw doll. Then, Kyoko enters in and accuses her of stealing her money, but Honda tries to act innocent. Kyoko states that she knows through her journal, but the nurse taunts with her, and destroys the journal. She leaves, taking the straw doll, and Kyoko cries out in anguish. Honda dumps the journal and is about to throw away the doll, when Ai grabs her by the arm, demanding it back. Honda flashes a knife, but Ai takes it out of her hand, too, and she flees. Ai returns the doll to Kyoko, who now remembers in a flashback of summoning Hell Girl through Hell Correspondence. Then, Kyoko remembers who she has a grudge against; the nurse that let her daughter die, Honda. Kyoko starts having a hallucination of Mika and remembers how Honda treated her, and she pulls the string.
Ai prepares for her mission and heads out to collect the nurse. For the punishment, Ren pulls Honda out into the street as an ambulance races towards her, and hits her. The paramedics leave her behind, stating that she'll die anyway. The three assistants arrive and explain her faults, but Honda only cries out in pain. Ai appears, Honda recognizes her as the girl who possessed as Mika, and she is teleported to the ferryboat. While being ferried to hell, Honda realizes that Ai is really Hell Girl, and cries out in horror.
Back at Kazama residence, Ai watches as Kyoko is being fed by her husband, and the black fire symbol is seen on her chest. Wanyuudou explains that Kyoko has lost all her memories, and the other two believe it was for the best, and they welcome their mistress home.