Ayumu Yamato, younger brother of Sho Yamato, emerges early in the series as the group reenters the X-Zone. He begins as a hotheaded mountain biker whose daredevil antics and lack of restraint result in repeated mishaps during races. A pivotal shift occurs when Koei, a seasoned ninja rider, mentors him, instilling disciplined techniques that refine his chaotic energy into focused skill.

His heartfelt bond with Sho, whom he affectionately calls "Oni-chan," drives his ambitions. Motivated by admiration yet hindered by early insecurities and reliance on others, Ayumu gradually cultivates self-assurance. This growth accelerates upon obtaining the Idaten bike Imperial Dragon, a machine mirroring his vibrant nature with raw speed and signature "blast-off power."

Within the X-Zone, Ayumu forges connections—a steadfast camaraderie with Koei and a warm rapport with Kiku, Koei’s sister. His evolution shines through pivotal milestones: triumphing over Team X racers solo, earning recognition in the X-Zone’s hero ceremony, and contributing decisively to group efforts. Though the Imperial Dragon’s full potential remains untapped, Ayumu solidifies his place as a tenacious rider.

Once a sidelined observer, he rises to engage directly in high-stakes clashes. Post-adventure, his maturity surfaces through dedicated training with allies and competing in the MTB Multiple X Racing event. Retaining his spirited zeal, Ayumu balances it with sharpening tactical insight—a testament to his transformative journey from turbulent novice to composed contender.