Gennosuke Yumi leads the Photon Power Laboratory, a position he inherited after the death of his mentor, Juzo Kabuto. A former colleague of Dr. Kabuto and father to Sayaka Yumi, he specializes in photon energy research and robotics development, notably creating the Aphrodite A robot piloted by his daughter.

In Grendizer U, Yumi directs the laboratory coordinating Earth's defense against the Vegan Empire, overseeing Duke Fleed (Daisuke Umon) and Koji Kabuto. His colleague, Genzo Umon, serves as his second-in-command, with Yumi identified as Umon's senior (kōhai). Yumi adopts a cautious, pragmatic stance regarding Duke Fleed's alien origins and the Grendizer robot, contrasting Genzo Umon's enthusiastic acceptance. He voices concerns that Grendizer could threaten Earth and questions whether Duke shares human morality.

During a critical incident involving Rubina's crashed spacecraft and an attack by the Vegan agent Blacky, Yumi imprisons Duke, labeling him a traitor. He nearly extends this punishment to Koji and Sayaka when they intervene to defend Duke. His leadership encompasses tactical planning and resource management during conflicts. After sustaining injuries in a Vegan attack on the laboratory, hospitalization forces him to temporarily transfer command responsibilities to Genzo Umon.

His professional background includes studying mysterious ruins resembling Greek architecture, as seen in other Mazinger-related media. During one investigation, he witnessed Koji Kabuto discover the remains of the Olympian warrior Zeus, which Yumi later reconstructed into the Z Mazinger robot. His personality reflects intense dedication to scientific work and crisis management, though he historically neglected personal relationships, including his daughter's emotional needs.