Asuka Midorikawa is a central character in the 2005 film, portrayed as a young professional working as a journalist for a weekly magazine called Weekly ABBA. Her initial encounter with college student Takeshi Hongo occurs in a professional capacity when she interviews him for a story, unaware that this meeting will soon thrust her into a terrifying conspiracy involving the terrorist organization Shocker.

In her personal life, Asuka is engaged to Katsuhiko Yano, a colleague who shares her profession. Their relationship forms the emotional core of her journey, as she is deeply in love and looking forward to their future together. This happiness is violently shattered when she and Katsuhiko become witnesses to Shocker's inhuman activities. During a brutal attack by Shocker soldiers, Asuka discovers the lifeless body of her fiancé next to the unconscious form of Takeshi Hongo, whom she had previously known only as a polite college student. This traumatic event defines her initial role in the story, as she is left grief-stricken and convinced that Hongo is a murderer responsible for her fiancé's death.

Driven by a need for answers and justice, Asuka's personality is defined by her determination and courage. Rather than retreating in fear, she begins to follow Hongo, demonstrating a stubborn resolve to uncover the truth about why the man she once interviewed has become a killer. This pursuit of truth reflects her instincts as a journalist, though it is fueled entirely by personal tragedy. Her motivations evolve from a simple desire for vengeance and understanding to a more complex struggle to reconcile the horrific events she has witnessed with her own sense of reality.

A key turning point in Asuka's story comes when she encounters Hayato Ichimonji, a mysterious man who is the exact double of her deceased fiancé. This shocking reunion is fraught with confusion and suspicion. Hayato reveals that the name Katsuhiko Yano was an alias, but he conceals the deeper, more horrifying truth: that Shocker recovered his corpse and transformed him into a powerful cyborg soldier, the second Hopper, programmed to eliminate Hongo. Despite this deception, the feelings between Asuka and the man who now calls himself Hayato remain a powerful force, creating an internal conflict for him that ultimately leads him to betray his masters.

Asuka's role in the overarching narrative is primarily that of a catalyst and a witness. Her trauma serves as the immediate trigger for Hongo to fully rebel against Shocker and embrace his humanity. Later, her life is placed in direct danger when Shocker attempts to kidnap and transform her into an inhuman soldier, an act that galvanizes both Kamen Riders to set aside their rivalry and fight together as allies. She represents the innocent civilian population that the Riders seek to protect, and her personal connection to both protagonists humanizes their superhuman struggle.

Throughout the film, Asuka develops from a grieving, accusatory woman into someone who likely gains a fuller, though tragic, understanding of the events. Her relationships are the engine of the plot: her engagement to Katsuhiko Yano and her subsequent grief over his death, her initial hatred for Takeshi Hongo, and her complicated, emotionally charged bond with the cyborg Hayato Ichimonji, who wears her lost love's face. She has no superhuman abilities or combat skills, as her significance comes entirely from her emotional resilience and her place at the center of the conflict between the two Riders and Shocker. Her character serves to anchor the film's more fantastical elements in a grounded sense of personal loss and romantic tragedy.