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"The Ephemeral" is the 26th and final episode of the season "Hell Girl".
Ai wakes up in her ferryboat, being taken to hell, and the Spider is angry at her for unleashing her rage upon the Shibatas. Ai states she must not go to Hell yet as she has something to do and is about to teleport away, but the Spider unleashes a web upon her. However, Ai tears it away and heads back to her birthplace in the mountains. The three assistants see their mistress return. Wanyuudou states that a powerful hatred is still binding her to this world. They fly away and follow her.
Back at the temple, Tsugumi asks Hajime why did Sentarou bury Ai, but sees that he has vanished. She then sees an image of the day she first saw Hell Girl at the train crossing. Ai asks if Tsugumi wants to know the story of a 'cruel man', but the young girl only wants her father. As the train passes by, Tsugumi's mother, Ayumi appears and the scene changes to a rainy night, when Hajime banished Ayumi from his household for betraying him and Tsugumi. Ayumi then takes off in her car and eventually crashes into a pole, dying in the process. Hajime arrives at the scene, but states it wasn't his fault for her suicide, and Tsugumi is heart-wrenched for what her father had done. Ai appears, sitting on a swing, stating that Hajime is a cruel man, and should have given his wife a second chance; but instead, he refused to admit his fault for her death. Ai then gives Tsugumi the black straw doll, but she doesn't want it; however, when she snaps out of the vision, she has it in her hands.
Hajime is found in the Twilight and learns of Ai's history from Ren and Hone. Ai's duty was to witness other people's hatred, and over time she locked away her own feelings and the memory of who she was, but all that changed when the Shibatas hunted her down, causing her painful memories to resurface. Then, Ai's grandmother speaks to Hajime, saying that she will help him escape from the Twilight, but on one condition.
Back at the Shibata's apartment, Tsugumi still has the doll but she refuses to pull the string. However, Ai insists that Tsugumi must do it to avenge her mother, even stating that Tsugumi hated her father the whole time; yet, the young girl refuses to believe it. Ai leaves out the door, but when Tsugumi opens it, one of Ai's ruby red eyes stare back at her, telling her to think carefully.
Much later, Tsugumi looks through her memories of her mother's death, but she still refuses to believe that Hajime was the one at fault. Just then, she sees the clock's hands run backwards and then sees Ayumi at the table with Ai behind her and delivers her speech. Tsugumi orders them to stop mocking her, but then Ayumi begins to bleed. Finally, they leave the poor girl in a state of tears. Then, Ai appears once again, and hands Tsugumi the doll and informs that she wants to relive her suffering. Just as Tsugumi reaches for the string, Hajime arrives with Ren and Hone, and the two urge to stop her torment on the Shibatas. Ai throws an energy blast at them, knocking them out. Hajime tries to escape with Tsugumi, but she steps away from him, stating of the night of her mother's death. Ai feeds more of the sadness into Tsugumi, even taking them to the past, where Ayumi was found dead in her car. However, unlike the past, this time Hajime states does in fact feel guilty for Ayumi's death and apologizes for making her lonely and having to grow up without her mother. Then, he adds more about his anger towards her when she betrayed him and Ai remembers her own anger when Sentarou and the villagers buried her.
Hajime tells Tsugumi to send him to Hell, but Tsugumi slaps him instead. She cries, caliing her father an idiot, and states that she doesn't hate her father and that even when she felt the loneliest she had always been happy with Hajime, showing that she still loves him. Ai is shocked at this and they are taken to the mountain stream with the blossom trees. Ai looks through her memories with Sentarou and Tsugumi gives the doll back to her. Tsugumi tells Ai that Sentarou actually loved her,and he deeply regretted his actions upon Ai that very night, so it was the reason why he built the "Seven Child Temple" in honour of her and the other children. They teleport back to the temple. Ai pauses, thinking about Tsugumi's words, then produces a fireball from her hands. In a fit of tears, she throws it at the temple, destroying it in a blast of fire, symbolically showing that she has forgiven Sentarou (as the temple was the symbol of his guilt). Ai leaves and her companions follow her. Tsugumi asks why did Ai destroy the temple, Hajime is about to answer, but he decides to head home with her.
After the closing theme, a scene of a modern city is seen which is in rain. The scene then jumps to a bruised girl, crying besides an unconscious and possibly dead cat in a rainy alley. Ai is then seen giving Wanyuudou as a straw doll to the girl while saying "The rest is for you to decide".
- This episode has the same name as the ending theme song of this season.