Sayaka Yumi, daughter of Photonic Research Lab head Professor Gennosuke Yumi, pilots the female robot Aphrodite A. Initially built for peace, Aphrodite A later deploys weapons like the chest-mounted Oppai Missile System. As a secondary combatant behind Koji Kabuto and Mazinger Z, Sayaka develops a rivalry fueled by his dismissiveness and her own strong-willed personality. This dynamic reflects her portrayal as a liberated, modern woman challenging contemporary gender norms through assertiveness and nonconformity.

Following Aphrodite A's destruction in battle, Sayaka plunges into severe depression, experiencing hallucinations of the damaged robot calling to her. She recovers upon receiving command of the Venus A, an upgraded robot modeled after her appearance using a photograph taken without her consent. Venus A boasts enhanced capabilities: flight via a hair-mounted thruster, Koshiryoku Beam photon weapons, Z Cutter forearm blades, and an improved Oppai Missile System, yet remains vulnerable in combat.

In the Z Mazinger continuity, Sayaka shares a childhood friendship with Koji and trains under Toko Kabuto, developing skills sufficient to challenge him. Forcibly brainwashed by Ares to fight Koji, she is freed when the original Aphrodite intervenes. After Aphrodite suffers a mortal injury, Sayaka bonds with its spirit to pilot the remodeled Aphrodite A. She proves her combat effectiveness by defeating the Mechanical God Artemis and supporting Koji against threats like Cerberus and the Hell King Gordon.

Her relationship with Koji involves constant arguments and mutual reluctance to admit deeper care, often highlighted in life-threatening situations. She occasionally experiences jealousy, such as when Koji interacts with women like Misato, Boss's cousin. After the original series, Sayaka departs Japan with Koji to study abroad.

In later continuities like Mazinger Z: Infinity, set a decade after the original conflict, she leads the New Photon Research Center, overseeing Photon Energy applications for peace. She appears in sequels and spin-offs like Great Mazinger and Mazinkaiser, frequently maintaining her role as a supporting pilot and strategic ally. She also features in non-canonical works such as Mazinger Angels, operating within an all-female task force using advanced versions of the original mecha.

Throughout her appearances, Sayaka demonstrates intelligence, martial arts proficiency, and unwavering dedication to protecting others, evolving from a secondary pilot into a resilient and integral figure across multiple timelines. Her legacy endures through cameos in other Go Nagai series and broader media references.