Dr. Shinichirō Izumi leads the Daimobic research base, assuming command after the death of its founder, Dr. Isamu Ryūzaki, during failed peace talks between Earth and the Baam-seijin. He is the grandfather of Nana Izumi and became the adoptive guardian and primary father figure to Kazuya Ryūzaki following the murder of Kazuya's father, Isamu. Dr. Izumi personally instructed Kazuya in karate, a discipline that directly shaped the young pilot's combat style, which is essential for controlling Daimos due to its movement-synchronization system. His own skill in karate is considerable, holding a black belt, and he has demonstrated the ability to defeat Kazuya in practice duels.

As the head of Daimobic, Dr. Izumi oversees scientific research, defense planning, and the maintenance of the super robot Daimos. His duties include coordinating field personnel such as Kazuya, Nana, and Kyōshirō Yūzuki, as well as support staff including the robot Cairo and the nanny Okane. He is a capable scientist who contributed to the development of Daimos alongside his friend Dr. Ryūzaki and later collaborated with scientists like Dr. Douglas Banks to upgrade the robot's energy systems and weaponry, including the "Daimos-Light" enhancement. He is also responsible for managing the base's transformation into a mobile command center during critical missions.

Dr. Izumi is characterized by an easygoing, gentle, and nurturing personality, acting as a stabilizing and parental presence for the younger members of the Daimobic crew. Despite his serious responsibilities and dignified appearance, he has a childlike fondness for sweets, particularly lollipops, and treats his subordinates with a friendly, informal demeanor. While he rarely displays anger, he stands firm when his principles are challenged. His ethical stance is firmly rooted in a philosophy of peace and coexistence, which puts him in direct opposition to the militaristic and xenophobic General Miwa. Dr. Izumi consistently resists Miwa's attempts to seize control of Daimobic and Daimos, committed to using the robot solely for Earth's defense rather than for aggression against the Baam. This philosophy extends to his wholehearted support of Kazuya's relationship with Erika, a Baam princess, viewing their bond as a potential bridge to peace between the two species.

Throughout the story, Dr. Izumi's primary motivation is to find a diplomatic solution to the conflict while protecting Earth. He appeals to the United Nations to secure Kazuya's release when the pilot is unlawfully detained by General Miwa and gives speeches advocating for empathy towards the Baam. His leadership provides the Daimobic team with the moral and strategic independence to act on their own judgment in pursuit of peace. He endures significant hardship, including suffering severe injuries during an attack on his base and later relocating operations to a former Baam underwater facility, yet he continues to lead the defense of Earth. His resilience and commitment to his ideals are tested repeatedly, but he remains a steadfast advocate for coexistence, contrasting sharply with the warmongering factions within Earth's military command.