Nagisa Kanō starts as an ordinary Japanese high school student plagued by unexplained phenomena: a voice in her dreams and fleeting glimpses of a mysterious blonde figure. Her existence dramatically shifts when parasitic Cthulhu aliens target Earth for invasion. Chosen by Iczer-1 as the synchronization partner essential to pilot the Iczer-Robo mecha, Nagisa becomes a prime target for the aliens. They mutate her classmates into monstrous Vedims during a school attack and later infest her parents, transforming them into Delvittse creatures.

Initially passive and resistant to her role, Nagisa grapples with fear and trauma. Her reluctance persists even after being forcibly teleported into the Iczer-Robo. However, witnessing the Cthulhu pilot Cobalt kill her parents unleashes overwhelming rage. This emotional surge enables her first synchronization with Iczer-1, releasing the mecha's full power to destroy Cobalt. After Earth descends into a post-apocalyptic wasteland, Nagisa grows resilient. She rescues a young girl, Sayoko, and her mother from ruins, later using a defensive bracelet gifted by Iczer-1 to shield them from Vedim assaults. Her protective instincts intensify when Iczer-2 threatens Sayoko, strengthening her resolve in combat.

Nagisa's development culminates during her abduction by Iczer-2, who imposes mind control. Forced to battle Iczer-1, she briefly regains autonomy and makes a critical decision: she implores Iczer-1 to kill her to shatter the mental domination. This sacrifice allows her spirit to merge with Iczer-1, achieving perfect synchronization and enabling the final victory over the Cthulhu leadership. In the aftermath, Iczer-1 employs an ancient wish-granting machine to reset Earth's timeline. Nagisa is restored to her ordinary life with no memory of the conflict. A fleeting, unrecognized encounter with Iczer-1 remains her only residual link to these events.