Kyoshiro Yuzuki, born to Japanese parents who defied his maternal grandfather Ittosai Yuzuki by moving to France, endured tragedy when his father died in a truck accident. His mother subsequently became homeless and succumbed to illness, leaving Kyoshiro orphaned and forcing his return to Japan as a child to live with Ittosai. Resentful over his parents' struggles, Kyoshiro initially refused to acknowledge Ittosai as family, addressing him only as "sensei." Their strained relationship persisted until Ittosai nearly sacrificed his life for Kyoshiro, leading to reconciliation. Under Ittosai's guidance, Kyoshiro trained rigorously in swordsmanship, becoming proficient with the katana.

As a member of the Daimobic Base crew, Kyoshiro serves as the primary pilot of the Galva FX-II combat jet, providing crucial aerial support during battles alongside his best friend Kazuya Ryuzaki, pilot of the robot Daimos. An accomplished astronaut and skilled swordsman, Kyoshiro approaches the conflict with the Baam-seijin with pragmatism, often contrasting Kazuya's idealistic stance. He frequently mocks Kazuya over his romantic involvement with Erika, the Baam princess, citing it as a wartime distraction. This teasing stems from Kyoshiro's skepticism about relationships amid conflict, though he acknowledges that "the heart wants what it wants" and continues to assist Kazuya in reuniting with Erika.

Kyoshiro demonstrates fierce loyalty to Kazuya, particularly when Earth military general Miwa Sakamori questions Kazuya's allegiance or imprisons him. In one instance, Kyoshiro hijacked Miwa's base to free Kazuya, openly defying authority to protect his friend. His pragmatic outlook faced a severe test during a mission to Baam Asteroid City, where he witnessed Erika shoot Kazuya under duress. Believing this confirmed his biases against Erika, Kyoshiro escorted the injured Kazuya to safety while expressing vindicated anger. Despite this, he remained committed to protecting Earth and supporting Kazuya, participating in critical operations against the Baam leadership, including the final assault on Olban.