Keyne Acqua, born Princess Lashara of a galactic empire, was secretly swapped at birth with the granddaughter of a scientist developing a potent energy source. The Emperor orchestrated the exchange to control the energy, which required the scientist's true descendant as its key, an act involving the death of the Emperor's wife, Lashara's mother. Years later, as the scientist finished the energy source and designated the false Keyne its guardian, the Emperor targeted her for capture. Fleeing pursuers in a spacecraft, Keyne crash-landed on Sandy Planet (Geminar) after an attack by Papacharino Nanadan, entering suspended animation to survive.

She remained in stasis until accidentally awakened by Photon Earth, a local with immense strength. Photon doodled the word "idiot" (baka) on her forehead in marker, mimicking a prank from his childhood friend, Aun Freya. Unaware, this mark held deep cultural significance in Keyne's society, symbolizing a marriage proposal. Interpreting it as a marital crest, Keyne accepted Photon as her husband, driven by fear of isolation and growing emotional attachment.

Initially pragmatic and opportunistic, Keyne seemed to exploit Photon's protective nature and her perceived marital status for survival and advantage, leveraging his strength against pursuers like Papacharino. Her character evolved into a genuinely caring and emotionally invested partner, developing authentic affection for Photon despite his obliviousness to their bond. Her personality blended resourcefulness with emotional vulnerability, frequently clashing with Aun Freya, who saw Keyne as a romantic rival. Their rivalry involved competitive behaviors like cooking contests and mutual taunts over physical attributes, showcasing Keyne's pride and pettiness.

Keyne wielded two primary weapons powered by Ahou Energy: a thigh-mounted flight band and a right wrist bracelet firing energy bolts. These were essential against adversaries like Papacharino seeking the energy source for galactic domination. She faced psychological and physical challenges, including temporary brainwashing by the galactic Emperor forcing her to violently attack Photon. Despite such ordeals, her resilience and loyalty to Photon defined her character arc.

Her development culminated in accepting her feelings for Photon and solidifying their bond, with the accidental marriage ritual repeated at the story's conclusion to reaffirm their union. Novel adaptations added depth to her relationship with Ahou Energy and featured slightly altered resolutions, while core character traits remained consistent.