"Classmates should stick together, not kill each other."

- Mr. Chibiki to Izumi Akazawa after she fatally wounded Tomohiko Kazami

Tatsuji Chibiki (ちびき たつじ, Chibiki Tatsuji) is a librarian at Yomiyama North Middle School. 26 years ago, in 1972, he was the homeroom teacher for the 9th Grade Class 3-3.

Mr. Chibiki has a very mysterious demeanor. In the anime, Kōichi Sakakibara and Reiko Mikami describe him as "The Lord of the Library." He claims that he ran away because he felt guilty and was afraid for his life, so he became a librarian instead of a teacher to avoid the class' curse. He decided not to leave, because running away was not the answer for him. He is always serious. In Another 0 chapters, Ryōko Akiyama claimed that he is not really friendly. He always dresses in black (anime notwithstanding), has an emotionless expression, and is not easy to get along with. Despite this, he can be brave when he needs to be, such as when he risks his life to save the students from the burning inn.

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Mr. Chibiki's appearance differs greatly in the anime and manga. In the anime, he is an old man with white hair that reaches past his shoulders and black eyes. He also wears spectacles with circular lenses. In the manga, his hair is much shorter. In Another 0 chapters, in his younger days, he had dark hair.

In Another 0 chapters, in 1983, when Reiko Mikami couldn't reach a book, Mr. Chibiki helped her. Later, Reiko asked for his help to stop the calamity, but he said that he didn't know a way to stop it. He is often seen in the library and occasionally talks to Mei Misaki there.

In "Face to Face", Mr. Chibiki tells Kōichi Sakakibara and Mei more about the curse and how the Misaki from 26 years ago was, in fact, a boy. He also informs them that he is an ex-teacher who taught Class 3-3 in 1972 and ran away, becoming a librarian because of the fear that he would die.

In "Build Limbs", he mentions hearing of Kōichi's mother's death, and then Kōichi tells him the when and where of it. He hadn't previously known that Ritsuko was one of the Class 3-3 calamity deaths.

In "Sphere Joint", Mr. Chibiki takes charge of the situation after Shoji Kubodera commits suicide, ordering Ms. Mikami to call the police and get the remaining students out of the classroom. Later, he remarks to Kōichi and Mei that Mr. Kubodera had seemed unstable when both arrived at the school that morning, and he had heard from the police that Mr. Kubodera had killed his mother before coming to school. Later still, both Izumi Akazawa and Ms. Mikami consult him about countermeasures.

In "Body Paint", after Junta Nakao's funeral, Mr. Chibiki tells Kōichi and Mei about how Junta's death, even if it happened outside Yomiyama, was caused by an event that occurred in Yomiyama.

In "Glass Eye", Kōichi shows Mei his mother's class photo. The purpose is to look for Misaki Yomiyama, but Class 3-3's teacher at the time, Mr. Chibiki, is plainly visible in the middle of the photo. (The same was also true in "Build Limbs" when Mr. Chibiki asked Kōichi which girl in another class photo was his mother.) Mr. Chibiki accompanied Class 3-3 on their trip to the Yomiyama Shrine. When Daisuke Wakui suffered an asthma attack during dinner, Mr. Chibiki asked everyone to call 119, but there was no signal. He then took Daisuke to the hospital.In "Makeup", Mr. Chibiki is shown driving down the mountain with Daisuke in the car.

In "Stand by Oneself", Mr. Chibiki arrives back just in time to save Yūya Mochizuki and Naoya Teshigawara from the crazed Keiko Numata, turning her knife on her and killing her. He takes Yūya and Naoya to his car, where he finds Matsuko Arita, who had made her way there after getting thrown through a window by an explosion; he asks her if she's the only one who's made it out, and she nods. He treats Naoya's injured leg, then tells them to stay there as he goes into the inn to help any students he finds. Though not shown, he freed San Watanabe, Sayuri Kakinuma, and Yukito Tsuji, who were trapped under a chandelier, and got them out. Mr. Chibiki also stops Izumi Akazawa from killing Tomohiko Kazami, saying that classmates shouldn't kill each other. Later, he got Kōichi and Tomohiko out of the building.

Days after the trip, Mr. Chibiki heads to the Mikami family grave to place flowers, and overhears Kōichi and Mei say there were eight deaths in August. He clarifies that a total of ten died due to the calamity in August; besides the eight students, there were the managers of the inn, who were Ikuo Takabayashi's maternal grandparents, who'd been depressed ever since his death. He then confirms that Ms. Mikami was the Extra, and after offering to drive Kōichi and Mei home, which they turn down, he tells them good luck and walks away.

"You should not be doing these terrible things ... like killing your classmates."

"There is no curse, there is no evil. Occurs naturally like a typhoon or an earthquake."

"This is not normal."