Kojirō, a young ninja of the Fūma clan, stands as the central protagonist across multiple adaptations. Charged with defending Hakuo Academy against the rival Seishikan and their Yasha clan allies, he confronts external threats through martial skill and unwavering clan loyalty. Wielding a wooden sword and ninjutsu, he epitomizes shōnen virtues—unyielding resolve and a firm moral compass—frequently locking horns with pragmatic foes like Musashi Asuka, driven by personal stakes rather than ill intent.

Rooted in the Fūma clan’s ancient allegiance to the Hōjō family, he reignites a centuries-old feud against the Yasha. The rivalry erupts into cosmic clashes over sacred swords, ensnaring Kojirō in a 4,000-year war cycle between Cosmo and Chaos. These trials upend his grasp of destiny, as the blades embody raw power and the inescapable recurrence of strife, shaped by Buddhist tenets of karma and rebirth.

Later arcs ignite internal Fūma strife when the "New Fūma Clan" splinters off, orchestrating a coup. This schism thrusts Kojirō into confronting betrayal and fractured ideologies, straining his allegiance to ancestral traditions. Adaptations deepen his emotional spectrum through bonds with Hakuo’s acting principal Himeko Hōjō and Musashi’s sister Erina Asuka, grounding his battles in human connection. These ties unveil his empathy and fragility, particularly when faced with comrades’ losses.

His evolution diverges across media: early tales highlight brutal skirmishes and clan fealty, while subsequent arcs wrestle with free will versus cosmic determinism. Spin-offs like the live-action series weave in scholastic life and deliberate character dynamics, showcasing his growth beyond battlefields through evolving alliances. His path culminates in lingering questions about eternal conflict, inviting reflections on perseverance and heritage.