Justin Kaidō, originally named Jin Kaidou, is the adoptive grandson of politician Yoshimitsu Kaidou, following his biological parents' deaths in the Tokyo Bridge collapse nine years before the main events. Initially introduced as a reserved and technically gifted LBX player dubbed the "Split Second Killer Emperor," his early demeanor reflected a quiet intensity and preference for solitude, partly shaped by his high-society upbringing. Over time, interactions with rivals like Ban Yamano fostered greater openness and camaraderie, softening his initially distant personality while maintaining his direct communication style and low tolerance for trivialities. Physically, he features pale skin, red eyes, and black hair with a distinctive grey-white streak on the right side. His appearance evolves across the series: a formal black-and-purple suit marks his debut; casual teal shirts and a puffer vest during his time with LBX Triton; and finally, a navy jacket, silver pendant necklace, and longer hair styled over his shoulders in his late teens. This visual progression aligns with shifting roles—from elite Innovator agent to defector, then Seeker and NICS ally, and later Cyber Lance test player and Harness vice-commander. His LBX expertise centers on high-speed, precision-based models. Primary units include The Emperor and its upgraded Emperor M2, noted for the "Impact Kaiser" finishing move. During tournaments and missions, he temporarily piloted units like Musha and Ikaros Zero. In his mid-teens, he adopted Triton, reflecting a tactical shift toward agility. By age 18, as Harness' vice-commander, he commanded Proto Zenon and Zenon, emphasizing advanced combat analytics. His battle record includes runner-up placements at Angra Visdas and Artemis (2050), finalist spots at Akihabara Kingdom and Artemis (2051), and victories against elite opponents like Lex and Hanzou. Key relationships define his arc: loyalty to Yoshimitsu, strained by the latter's morally ambiguous schemes; a rivalry-turned-friendship with Ban, culminating in alliances against threats like the unstable Yuuya Haibara; and a protective bond with Yuuya, evident in post-battle care and collaboration. The manga spin-off *Jin Kaidou Gaiden* highlights his early complexity—dismissive of civilian LBX enthusiasts yet self-reflective after harshness, ultimately intervening to shield a girl from a rogue LBX despite initial reluctance. His narrative spans critical turning points: defecting from Innovator after witnessing their manipulation; aiding Ban in freeing Yuuya from Psycho Scanning Mode during the Artemis finals; and participating in cross-world crises, as seen in the *Inazuma Eleven GO vs. Danbōru Senki W* film. By *Wars*, his role shifts toward leadership and mentorship within Harness and later Jenock, tracing a trajectory from isolated prodigy to dedicated protector.