Mayu Akikawa is a clinical psychologist working at Kurokawa Memorial General Hospital in Tokyo. She is introduced as Dr. Mayu Akikawa, a psychology counselor assigned to a young girl brought in by police after a fire at a public housing complex. The girl is suffering from amnesia and cannot remember her own name, only that her mother called her Sadako. Mayu quickly becomes deeply involved in the girl's case, both professionally and personally.

Mayu's background is marked by hardship. She and her younger brother, Kazuma, were abandoned by their parents during elementary school and grew up as orphans. This shared experience of isolation and loss shapes her worldview and fuels a strong protective instinct toward her brother. She is responsible and diligent in her work, often going beyond routine care to connect with her patients. Despite her professional composure, she carries a sense of worry about Kazuma, who dropped out of programming school and now tries to build a following as a YouTube personality.

Her primary motivation is to protect those she cares about. When Kazuma goes missing after investigating the burned apartment building, Mayu becomes determined to find him. Her search leads her to uncover the truth behind the resurrected curse of Sadako Yamamura, a vengeful ghost from the Ring franchise. She travels to Oshima Island with web marketing consultant Yusuke Ishida, explores a cave shrine where unwanted infants were abandoned, and learns that Sadako feeds on the souls of these abandoned children. Mayu's experiences cause her to question whether she and Kazuma were also drawn to Sadako as lost souls.

In the story, Mayu serves as the protagonist who connects the modern-day mystery to the legend of Sadako. She is the one who pieces together clues from online videos, hospital records, and the testimonies of patients like Masami Kurahashi, who recounts Sadako's origin. Her role is that of a determined investigator and a compassionate caretaker.

Key relationships include her bond with the mysterious girl. Mayu sees a reflection of her own lonely childhood in the girl, and she becomes the only person who treats the girl with genuine kindness and trust. This emotional connection allows Mayu to reach the girl in a critical moment inside the cave, where she embraces the girl and urges her to fight back against the drowning spirits. Another crucial relationship is with her brother Kazuma. Their sibling bond is the emotional core of the film; Kazuma ultimately sacrifices himself by allowing Sadako to drown him in order to save Mayu. Mayu's relationship with Yusuke Ishida is largely cooperative, as they work together to investigate the curse.

Mayu undergoes significant development over the course of the narrative. She begins as a competent but somewhat reserved professional, focused on her patients and worried about her brother. As the supernatural threat escalates, she becomes more proactive, venturing into dangerous locations and confronting terrifying visions. Her fear is evident, but she pushes through it for the sake of the girl and her brother. The climax of her development occurs when she embraces the girl in the cave, an act of pure empathy that temporarily breaks the curse's hold. In the aftermath, she is shown recovering in the hospital, only to be killed by Sadako in her room, making her a tragic figure whose compassion ultimately could not save her.

Mayu has no supernatural abilities. Her notable traits are her psychological insight, her empathy, and her resilience. As a clinical psychologist, she is trained to listen, observe, and analyze behavior, which helps her understand the girl's trauma and the pattern of the curse. She is also physically brave, willing to enter a cave shrine and face the ghost directly. Her greatest strength is her emotional capacity to connect with others who are suffering, which allows her to offer comfort even in the face of death.