Genbu, one of the four Kitoralsus agents from the Underground World, begins as an antagonist. Driven by curiosity about human capabilities and their giant robots, he openly confronts the Shinkansen Ultra Evolution Institute and their Shinkalion units, voluntarily assuming a Giant Monstrous Being form. He consistently overpowers the Shinkalions until the N700A unit intervenes and shifts the battle's momentum.

Following his defeat, Genbu is temporarily placed under the protection of the institute's Ōmiya Branch. He maintains silence about his origins but explicitly states he holds no hostility toward humanity. Human characters, including Azusa Ueda and Akita Oga, work to build trust and encourage him to share information about the Underground World. Later, external forces forcibly manipulate him back into his Giant Monstrous Being form. Resisting this control, he intentionally creates an opening during combat, enabling the Shinkalion E5 to deliver a decisive point-blank Gran Cross attack. This act of defiance leads to his eventual alliance with the institute around episode 55.

Approximately three years later, during the conflict with the Teoti in *Shinkalion Z*, Genbu strategically assumes his monstrous form again. He acts to buy time for the deployment of new Z-unit Shinkalions, sustaining a significant arm injury during a calculated bluff against Astrea's infiltration of the Ōmiya Branch.

In the final phase of the plan to defeat Arabaki, Genbu willingly transforms alongside the Shinkalion Z units and the Monsterized Teoti Warriors—former adversaries temporarily allied with humanity. Together, they target and destroy Arabaki's roots, demonstrating his full integration into the institute's efforts.