Kiichi Inukai functions as the fictional academic figure and primary narrator within the film. Rendered as a diminutive 3D CGI animated professor with caricature-like features, he serves as a comedic, occasionally slapstick framing device to deliver the documentary's content. He conducts his lecture aided by his silent, clumsy female assistant Iori, whose exaggerated mishaps and visual gags provide physical comedy, injecting humor into the dense historical exposition.

Inukai delivers information in a rapid-fire style, covering topics far beyond Musashi's life, including comparative analyses of European knights, Japanese samurai, Chinese cavalry tactics, the evolution of warfare technology (like WWI tank introductions), and the political reinvention of the Musashi legend during the Russo-Japanese War. He presents controversial arguments, challenging popular myths from Eiji Yoshikawa's novel by emphasizing Musashi's real-life traits: his left-handedness, preference for smaller swords, unmentioned duel with Sasaki Kojiro, multifaceted talents in arts and civil engineering, and lifelong ronin status. Inukai also posits that "The Book of Five Rings" may have been partially intended as a tool for securing patronage.

His lecture incorporates diverse multimedia elements: traditional 2D animated battle reconstructions, live-action footage of historical locations, and stylized segments resembling strategy games or historical diagrams, reflecting the film's experimental narrative structure. This character's design and purpose root in demystifying Musashi, positioning him as a universal genius comparable to figures like Leonardo da Vinci rather than solely a legendary swordsman.