Thirty years before the events of Ring, a 19-year-old Sadako Yamamura joins an acting troupe as an understudy, hoping to escape her traumatic past and the uncontrollable paranormal powers she has inherited from her mother, the famed psychic Shizuko. While struggling to control these abilities, she finds a sense of belonging and begins to fall in love with the troupe's kind sound director, Hiroshi Toyama. However, her presence coincides with a series of disturbing events. After the lead actress, Aiko, is mysteriously killed by a ghostly figure in white, Sadako is promoted to the starring role, further alienating her from the other members who grow to fear and distrust her.

As Sadako and Toyama's relationship deepens, a journalist named Akiko Miyaji closes in on the troupe. Miyaji is investigating Sadako, believing her to be responsible for the death of her fiancé, a reporter who was killed during one of Shizuko’s disastrous public demonstrations years ago. Photographs taken of Sadako reveal a ghostly double, confirming the existence of a second, malevolent Sadako who is responsible for the violent murders. This dark twin, a being of pure rage that resembles the father Sadako never knew, has been secretly contained by her foster father, Dr. Ikuma, in his attic.

The troupe’s paranoia reaches a fever pitch during the final performance, triggered by a recording of Sadako's mother. The innocent Sadako is overwhelmed by her powers, leading to a violent confrontation in which the terrified troupe members corner her and beat her to death. Believing the threat is over, the group learns from Dr. Ikuma that they have only destroyed Sadako’s gentle human half. The malevolent entity, now free, merges with the corpse of the innocent Sadako, resurrecting her as a unified, vengeful specter. She systematically hunts down and kills every member of the troupe, including the horrified Toyama, leaving no survivors.

In the aftermath, a remorseful Dr. Ikuma finds a weeping Sadako, who has temporarily returned to her human form, grieving her actions. Recognizing the danger she poses, he drugs her and brutally attacks her with an axe before throwing her body into the deep well on his property. As the heavy stone lid is slid into place, sealing her in the darkness, Sadako screams, awakening to her fate. Abandoned and trapped at the bottom of the well, her sorrow and rage begin to fester, marking the true birth of the terrifying onryō who would one day create the cursed videotape.