Sadako comes from the protagonist in the Japanese science fiction novel The Circle and its adaptation of the horror film The Ring of Midnight. The appearance of Sadako comes from the cursed video, and Sadako is also one of the well-known terrorist figures.

Sadako was born in Izu Oshima, Japan in 1950s. She is the child of Shizuko Yamamura and Kazuo Hirai, an assistant professor of psychiatry at Oshima University in Tokyo. When Shizuko was hospitalized with a headache, she met Hirachi Langyixiong. Her headache has something to do with finding a statue called Kamakura from the ocean, and it also gives Shizuko the ability to predict the future.

After discovering Shizuko's super power, Hirashiro was very interested, so he conducted a study on Shizuko. Then Shizuko gave birth to a daughter. Because Hirashiro didn't get divorced, the child was named "Sadako Yamamura" after her mother's surname. Shizuko later gave Zhenzi to her grandmother to take care of and returned to Tokyo by herself. When Sadako was 3 years old, her mother came back and left Oshima with Sadako.

Zhen Zi's ability: Zhen Zi's all abilities include: immune physics, infinite resurrection, teleport, surpassing ordinary people's strength, prediction, treatment, infinite doppelganger, channeling, mind control, gravity control, hair control, thinking control, fear control, dream control, time and space control, reality distortion and so on.

In the whole process of "Midnight Ring" series, Zhenzi showed the great spiritual strength of ghosts when she was alive. After Sadako's death, she was a supernatural spectre of revenge, with long black hair, which covered the traces of her face and nails and gave off more destructive spiritual strength. In the game between Zhenzi and Kayako, her strength was stronger than before.