Saori Ōtaki is the daughter of scientist Kyōtarō Otaki and the older sister of protagonist Daigo Ōtaki. After their father's death, she secretly managed Victor City (or Victor Town), a planned settlement established to preserve humanity following Earth's devastation by a global cataclysm triggered by a radioactive meteor's approach. Her responsibilities encompassed overseeing the city's operations and safeguarding its advanced technology, especially the Gordian robotic defense system created by her father.

She later encountered Daigo, who had been raised separately by their uncle, revealing his true heritage. Saori pleaded with him to inherit the Gordian system, stressing it was their father's legacy. The system was genetically encoded to Daigo's DNA, designating him as the sole viable pilot. Saori's own attempt to pilot Gordian resulted in severe burns and life-threatening injuries due to her incompatible DNA.

Following this event, she transitioned into a strategic advisory role. She provided vital intelligence on the Gordian system's capabilities and Victor City's hidden technologies, including the super energy substance Ixtron, a target for the antagonistic Madokter Army. She also supported the Mechacon combat unit defending the city.

After the Madokter Army occupied Victor City, Saori evacuated to Fort Santore with other survivors. There, she continued aiding resistance efforts by coordinating resources and personnel, helping establish Santore as a new base of operations. Her leadership extended to managing the Anoh, a mobile command center essential for counteroffensives against the invaders.

Her relationship with Daigo evolved from an initial distance—rooted in their childhood separation—into mutual trust. Early drafts of the series conceptualized her with the Western name "Sara," revised to Saori Ōtaki in the final version to emphasize her Japanese heritage.