Sonosuke Nakajima, a lieutenant general in the Imperial Japanese Army, hails from a Saga Prefecture samurai lineage. He founded Code Zero, a military unit initially dedicated to information warfare before pivoting to confront the vampire crisis. Driven by Japan’s catastrophic Siberian losses, he seeks to forge an immortal army of vampire soldiers through Ascra—an artificial blood substitute—to eradicate human vulnerability on the battlefield. His fixation on military progress justifies ethically ambiguous experiments, including forcibly transforming soldiers into vampires.

His bond with Yoshinobu Maeda, whose life he saved in Siberia, anchors Maeda’s fierce loyalty. This allegiance fractures when Maeda uncovers Nakajima’s covert experiments, notably the transformation of his actress daughter, Misaki, into a vampire after she exposed his collaboration with foreign operative Rufus Glenn. A staged accident mortally wounded Misaki, yet Nakajima denies her vampiric existence, subordinating familial ties to military ambitions—a choice that deepens Maeda’s disillusionment.

The Great Kantō Earthquake cripples Nakajima’s infrastructure, destabilizing his operations. His rigid deference to hierarchy and contempt for leadership devoid of battlefield experience reflect an uncompromising militaristic ethos, yet his extremism erodes alliances. The unchecked spread of vampires and Ascra’s destabilizing side effects ignite public chaos, amplifying societal fractures.

Though a strategic innovator, Nakajima’s failure to reconcile his vision with its moral and logistical fallout cements his tragedy. His legacy intertwines military and social upheaval with personal ruin: Maeda’s vampiric transformation, Misaki’s death, and the collapse of trust among those ensnared in his relentless pursuit of immortality.