Chapter 1-4
When the students of Kisaragi Academy enter Heavenly Host Elementary School after performing the "Sachiko Ever After" charm, Sachiko remains mostly in the background, allowing other sources to kill the students.
She appears before Naomi, Seiko Shinohara, Satoshi, Yuka, and Ayumi during their travels through the school.
The group learns through newspaper clippings that Sachiko is a former student of Heavenly Host in 1953, and one of the recorded victims of the 1973 serial kidnappings and murders at the school and also, the only survivor.
Chapter 5
On the day of her birthday, Sachiko went to see her mother, Yoshie Shinozaki, after school.
While heading up to the third floor, she witnessed the principal, Takamine Yanagihori, push her mother down the stairs after his attempt to rape her, thus snapping her neck and killing her.
Afraid of Sachiko telling someone about what he did, Takamine chased her through the school and captured her, strangling her to death over the corpse of her mother.
Takamine told the police that Yoshie's death was an accident, and buried Sachiko in the basement of the school building.
Sachiko was soon noticed to be missing, but her body was never found and thus her death was never actually official.
Unable to find peace after being killed in such a brutal, heartless manner, Sachiko's spirit remained in the school.
At some point, she began infiltrating Takamine's thoughts, driving him to madness.
He, believing she might still be able to tell others about him killing Yoshie, cuts out her tongue to prevent her from speaking out about it.
Some 20 years later, Sachiko once more gained a corporeal form.
She used Yoshikazu Yanagihori, Takamine's son and teacher at the school, who, like his father, was driven to madness, to capture children for her to kill and send to her mother.
She eventually stopped killing for her mother's sake, and simply did it because she enjoyed it.
The only notable killings she did were those of Ryou Yoshizawa, Tokiko Tsuji, and Yuki Kanno.
After performing the killings, she pretended to be one of the kidnapped students, and framed Yoshikazu.
She fingered him as the killer, and he was sent to a mental hospital, while she was allowed to fade away without anyone noticing, as they were all preoccupied with the "murderer."
After the demolition of the school, an alternate dimension kept together by the souls of Ryou, Tokiko and Yuki exists where the school is still standing.
Her and the other ghosts, along with Yoshikazu, who killed himself after escaping from the hospital and was also brought to the cursed dimension, kill whoever enters.
Eventually, when the students reach Sachiko's body in the basement and succeeded in appeasing her, returning her tongue and giving her the black cat plushie Yoshie bought her for her birthday, allowing her to rest in peace at long last.
Giving Yuki control of the school as the "New Sachiko."