Natsumi Ueno is a university student who becomes one of the central victims in the events of the film. She and her best friend Yuri Kurahashi purchase a used video player from a recycle shop, unaware that it contains a cursed videotape. When the two friends play the tape out of curiosity, Yuri is distracted by her phone, leaving Natsumi to watch the entire disturbing footage. This act marks her as a target of the vengeful spirit Sadako Yamamura, with the curse's deadline shortened to two days.

In terms of personality, Natsumi is described as kind and funny, but also notably cowardly. Her initial reaction to the curse is one of overwhelming terror, and she becomes increasingly desperate as the deadline approaches. Her primary motivation is survival: she wants to escape the fate that has befallen others who viewed the tape. This fear drives her to take drastic actions, including uploading the cursed video onto the internet, hoping that spreading the curse might somehow save her. When that plan fails to bring relief, she sinks into despondency and attempts suicide as a way to regain control over her imminent death.

Natsumi's role in the story is that of a catalyst. Her cursed condition sets the main plot in motion, forcing Yuri, their professor Shinichi Morishige, and eventually the psychic Keizo Tokiwa to search for a solution. Her worsening state demonstrates the relentless nature of Sadako's curse and raises the stakes for everyone involved. She also serves as a source of emotional weight, as her friendship with Yuri becomes strained when she blames Yuri for not watching the tape alongside her.

The most important relationship in Natsumi's life is her close friendship with Yuri. They are university classmates and share a bond strong enough that Yuri later watches the tape herself, hoping to transfer the curse away from Natsumi. Natsumi also interacts with Professor Morishige, whose obsession with urban legends leads him to watch the tape as well, and later with an exorcist, but these connections are brief and end in tragedy.

Natsumi's development over the course of the film is a downward spiral from ordinary life into paralyzing fear. She starts as a normal young woman, but the curse erodes her composure and rationality. By the end, her actions are driven purely by panic and a desire to escape, culminating in a failed suicide attempt. She possesses no supernatural abilities; her significance lies entirely in her vulnerability and the choices she makes under duress. Her death occurs when Sadako appears before her and kills her by hanging, even as Yuri rushes to save her. Natsumi's fate underscores the film's theme that the curses of Sadako and Kayako are inescapable for those marked by them.