Nagisa Kano, a high school student yearning for a quiet existence, finds her world shattered when Iczer-1, a rogue android, forcibly recruits her as a synchronization partner to combat the alien Cthuwulf invasion. Traumatized by the deaths of her parents and classmates—transformed into grotesque monsters by Cthuwulf parasites—she initially rejects Iczer-1, holding the android responsible for the devastation.

Her resistance, rooted in grief and fury, softens after encounters with Sayoko, a child survivor whose fragility mirrors humanity’s precarious state. Compelled by the escalating threat, Nagisa reluctantly bonds with Iczer-Robo, a mechanized warrior whose synchronization process fuses their minds and bodies, shedding her civilian identity—literally and symbolically—as she merges with the machine.

Though her rage against the Cthuwulf hardens her resolve, vulnerability lingers. Manipulated by the rival android Iczer-2, Nagisa turns on Iczer-1 in a brainwashed frenzy, only to reclaim agency in a desperate act of self-sacrifice, begging for death to halt the invasion. This moment cements her tragic alliance with Iczer-1, intertwining their fates.

Victory arrives at a cost: Iczer-1 rewrites reality, erasing the invasion and restoring Nagisa’s family and mundane life. Her memories vanish, leaving no trace of the war or her bond with Iczer-1—a bittersweet return to innocence.

Decades later, Nagisa’s legacy resurfaces through her granddaughter, Nagisa Kasumi, who inherits fractured echoes of her grandmother’s battles. Partnering with Iczer-3, a next-generation defender, Kasumi reignites the cycle of resistance, ensuring Nagisa’s shadow endures in humanity’s unending struggle against cosmic threats.