Lieutenant General Sōnosuke Nakajima commands the Japanese Imperial Army’s experimental Code Zero unit, directing vampire soldiers against supernatural threats while advancing Japan’s military supremacy. Forged by a catastrophic defeat in Siberia, his pragmatism prioritizes national security over moral boundaries, driving him to pioneer artificial blood sources like Ascra through alliances with foreign scientist Rufus Glenn. This synthetic sustenance enables mass vampire conversion, though unstable results plague the program.

Nakajima’s strategic calculus extends to personal bonds: he groomed protégé Yoshinobu Maeda after rescuing him in Siberia, cultivating loyalty tested by clashes between expediency and conscience. His familial ties fracture when daughter Misaki uncovers his vampiric experiments, leading to her fatal injury, forced transformation, and subsequent mental unraveling. Her death destabilizes Code Zero, compounding challenges from the Great Kantō Earthquake’s destruction of critical facilities.

Balancing tactical ingenuity with ethical compromise, Nakajima rationalizes human experimentation and political subterfuge as sacrifices for Japan’s dominance. Yet his inability to reconcile cold ambition with human connections erodes alliances, including the collapse of his partnership with Glenn. The implosion of his vampire-army project ultimately mirrors his own downfall, exposing the peril of sacrificing humanity for power.