Saijō Sogo is the coordination commander of the Shinkansen Ultra Evolution Institute's Yokogawa branch, overseeing operations and personnel that combat giant monstrous beings using transforming train robots called Shinkalion Z units. He possesses a naturally timid, nervous, and frequently anxious personality, often appearing overwhelmed by his duties. Despite this, he remains fundamentally well-intentioned and is described as "impossible to hate." His leadership style differs markedly from previous commanders, frequently seeming bumbling and ineffectual in critical moments, which affects team dynamics and operational efficiency.

During the series, Saijō Sogo encounters significant challenges, including his abduction by the antagonistic group Teoti. This occurs when Teoti infiltrates the Yokogawa branch, exploiting his vulnerabilities and using him as leverage for their goals. His role centers on administrative coordination and responding to emergent threats alongside mechanics like Goichi Shima and child drivers such as Shin Arata and Abuto Usui. Information regarding his background, family, or life outside the institute remains undocumented. Official media, including films, OVAs, or spin-offs beyond *Shinkalion Z*, does not feature his character development or further involvement.