"Chain Reaction" is the 24th episode of the season "Two Mirrors" and the 50th episode from total.
People are disappearing left and right in the town of Lovely Hills. After Mr. Mariyama goes home from Takuma's house, he is sent to hell by his daughter who hates him for scolding her. Another woman named Akiko sends her husband to hell because she regrets marrying him. Then Akiko's friend sends her to hell, because she's always hated Akiko. And so forth. All the disappearances are blamed on Takuma. While the disappearances are happening, Detective Meshiai goes to the library and finds the book written by Shibata Hajime about Hell Girl. After learning about Hell Girl from the book, he goes to Takuma's house and sees that Takuma doesn't have the Hell brand on his chest, and confirms that Takuma is innocent. Mr. Tsuyuki, one of the neighbors who has been keeping a vigil outside Takuma's house, attacks Detective Meshiai for discovering the truth. Before collapsing, Detective Meshiai sees the Hell brand on Mr. Tsuyuki's chest. In the meantime, Hotaru is at Ai Enma's house. After Enma Ai tells Hotaru that it's not up to her to decide who to send to hell, Ai brings Hotaru back to the mortal world.