Aoi Mitsukuni starts as a reserved 15-year-old Earth boy, ignorant of his extraterrestrial origins. After his father's early death, he believes his mother Mito works overseas as a model. In truth, Mito is an alien space pirate from a species with unique biology, including gender determination during puberty. Galactic Patrol officers pursuing Mito expose her secret, shattering Aoi's ordinary life and dragging him into galactic conflicts.

Initially uncomfortable with Mito's true childlike appearance, Aoi gradually adapts to cosmic adventures. He develops romantic feelings for Galactic Patrol officer Mutsuki Nenga, creating loyalty-driven tension. During a climactic battle against galactic ruler Ranban, Aoi experiences a species-based gender transformation, stabilizing as female. Simultaneously, Mito unexpectedly relinquishes her throne, elevating Aoi as galactic queen.

As queen in the second season, Aoi adjusts to her new gender identity while defending Earth and the galaxy from Hikari—a malevolent entity claiming rightful rulership with planet-destroying power. Aoi's leadership is tested as she organizes defenses, relying on allies like Mutsuki, though their relationship complicates due to Mutsuki's struggle with Aoi's transformation. Aoi ultimately defeats Hikari, establishes galactic democracy, and voluntarily steps down from monarchy. Her arc concludes with acceptance of her female identity and ongoing responsibilities.

Throughout both seasons, Aoi evolves traits of loyalty, courage, and a strong moral compass. Key relationships include her protective bond with Mito, romantic tension with Mutsuki, and adversarial-yet-redemptive connections with foes like Ranban and Masatsuki Nenga who become allies. Her design features dark brown hair, blue eyes, and a physical presentation shift from masculine to feminine reflecting her biological and narrative journey.