Saito acts as a high-ranking enforcer for Daiwa Heavy Industries under the command of Kisaragi. His origins remain obscure, though he was conscripted into a mandatory vaccination program during an orchestrated viral crisis that converted his body into bio-metal. This transformation eradicated his free will, cementing absolute loyalty to Daiwa’s pursuit of prohibited biotechnology.

During an initial clash with SWORD operatives in Colorado, Saito ambushes the unit with lethal precision, detaching his own leg to evade capture—an act that exposes his synthetic composition and sparks SWORD’s probe into Japan’s clandestine operations. Later, he spearheads the apprehension of SWORD agents infiltrating Japan, coercing intel from resistance figures like Maria to hunt down fugitive operative Vexille.

His allegiance to Kisaragi collapses upon uncovering his commander’s avoidance of the vaccination, leaving Kisaragi fully human. The revelation unveils Kisaragi’s hypocrisy in enforcing synthetic conversion as evolutionary progress while evading it himself. Consumed by fury, Saito assaults Kisaragi during a climactic duel at Daiwa’s headquarters.

Mortally wounded in the conflict, Saito expends his final strength to free Vexille and Maria from confinement. Though his defiance enables their disruption of Daiwa’s schemes, his rebellion stems not from reformed ideals but seething resentment over Kisaragi’s betrayal.