Masami lived in Tokyo and was friends and classmates with Tomoko Oishi, Yoko Tsuji and Iwata. While Tomoko's parents are out, Masami visits her at her home and they do homework while watching a baseball game on TV. Masami strikes up a conversation regarding the rumours of a mysterious cursed videotape and tells Tomoko that a young boy came to Izu and tried to record a sports event on television, but ended up recording an odd video where a woman warned him he had watched the tape and a week later he died.
Masami laughs at her own joke, but notices Tomoko is clearly disturbed. Tomoko tells her about their trip and reveals that they watched the said tape. However, she then tells she is joking and admits to Masami that she slept with Iwata. As the two playfight, the telephone downstairs in the kitchen rings.
Masami realises Tomoko was telling the truth and races downstairs to answer the phone to protect her. The two confront the phone. Masami answers it and quickly hands it over to Tomoko, who learns her mother has called. Masami collapses to the floor in a fit of laughter as Tomoko ends the phone call. Masami then heads to the toilet, leaving Tomoko alone. At this point, Masami returns to find a strange light flashing in the lounge, opens the door and sees Masami. To her horror, Masami kills Tomoko. The experience traumatised Masami and she is hospitalised, attending Tomoko's funeral.
A couple of weeks after the events of the first film, Mai Takano and Okazaki investigate the death of Ryuji Takayama and Reiko Asakawa's disappearance. They learn that Masami is still in hospital and decide to visit her. They meet her psychiatrist and doctor Ishi Kawajiri who has discovered Masami has inherited Sadako's Nensha powers, images from the videotape imprinting themselves on photos he took of her.
A nurse visits Masami in her room and suggests she takes a walk. Masami silently objects, but the nurse realises she is still scared of the television in the patients' activity room. The nurse guides Masami down a corridor using a wheeled curtain to block out the view of the television. However, Masami tries to overcome her phobia and steps out from behind the curtain and walks into the middle of the activity room to look at the TV. However, her psychic powers, obtained via her brief encounter with Sadako, begin to act up and cause images of the tape to appear on the TV, throwing the mental patients present to panic.
Masami collapses and spots Mai, asking her for help. Mai grabs her hand, and witnesses a flashback from Masami's point of view, seeing Sadako in the television. Terrified, Mai drops Masami's had. The girl cries "Help me!", what makes Mai recognize words which Yoichi mouthed to her earlier. It's revealed that were her first words since hospitalization, because like Yoichi, Masami became mute after the events present in the first movie.
Mai later visits the hospital again to talk to Dr. Kawajiri but is shocked to find Masami is being used in an experiment. Dr. Kawajiri explains he wishes to exorcise Sadako's influence from Masami via energy transfer, having Masami project the images in her mind onto a blank tape. Mai, Okazai, Dr. Kawajiri and Detective Keiji Omuta watch what unfolds, but the images of the tape are projected. A mass electrical surge sweeps through the equipment present, Dr. Kawajiri's nurse alerting Dr. Kawajiri to Masami. The two run to her, but Masami has passed out.
20 years later after the events of Ringu 2, it is revealed that Masami survived and recovered from her trauma. She befriends her therapist, Dr. Mayu Akikawa, although Dr. Fujii warns the latter that such a bond may be unhealthy. Indeed, it's revealed that Masami became obsessed in Mayu and stalked her, entering into Mayu's office at night without the latter's permission. When Mayu tries to cut the contact, Masami accuses her of ghosting her, then charges at her with a scissors.
Then a little girl with long hair emerges and stares at her creepily, before passing out. TV on the corridor turns on and Sadako crawls out from the screen. She charges at Masami, but loses her interest in her prey after noticing Mayu carrying the little girl. Sadako grabs Mayu, who also passes out.
The next day, Mayu, Masami and the girl are found by the hospital staff. Masami in the state of shock is admitted to the psychiatric ward again. Later, Mayu enters her room and interrogates her. Masami tells her the story of Shizuko and Sadako, and the latter's curse. Later that night, Sadako attacks Masami once more, dragging her under the bed with her long hair. There is heard Masami's scream, and the next day she's found dead under the bed, with distorted face, like the other Sadako's victims.