Hikaru Makiba assists her father, ranch owner Danbei Makiba, with farm labor and animal care in rural Japan. Her ordinary civilian life shifts when she encounters Duke Fleed, an alien prince hiding on Earth as Daisuke Umon after escaping his destroyed homeworld, Fleed. Discovering Duke's true identity and the threat of the Vegan Empire, she resolves to defend Earth, joining the fight despite Duke's initial objections.

She transitions into active combat by piloting the specialized Marine Spazer support vehicle, battling Vegan forces alongside Duke Fleed and Koji Kabuto. Hikaru adapts to military responsibilities while maintaining her civilian connections. Her emotional bond with Duke evolves beyond friendship, highlighted when he removes her wet clothes while she is unconscious to prevent illness; her lack of anger and understanding of his secret identity imply a deepening relationship. She reaffirms her commitment to him, continuing to use his Earth name "Daisuke" as a sign of acceptance.

In the spin-off *Grendizer Giga*, she interacts with a reimagined Duke (Daisuke Uryu), displaying protectiveness like defending him from bullies using a soccer ball. Her role retains core elements: connection to ranch life, determination to protect others, and involvement against extraterrestrial threats, though specific plot details diverge.

Across media, her journey depicts a shift from pastoral routine to wartime engagement, driven by loyalty and duty. Her interpersonal dynamics, especially with Duke, remain central to her character arc, emphasizing trust and resilience without supernatural abilities or drastic transformations.