Yuuji Tamiya is a soldier in the NOA unit of the organization CURE. He wields Nano Osmolar Armor and combat-enhancing nanomachines against virus-infected creatures. Witnessing heavy losses among his comrades fuels frustration when he learns CURE possesses but conceals Ai, a potential weapon against the threat. After contact with an infected creature, he undergoes quarantine and release, only for tests to reveal the virus has evolved to attack his nanomachines. CURE orders his arrest due to this infection, prompting his escape with Ai as hostage. His condition deteriorates during their time together until Ai uses her abilities to heal him. With help from fellow NOA soldiers, they evade capture before eventually being detained by CURE forces. Inside a NOA facility, he faces both infected former comrades—transformed as the virus destroyed their nanomachines—and hostile CURE units. Ai intervenes, eliminating the virus and resolving the conflict. Later, during a major outbreak where the virus mimics nanomachine capabilities, he delays advancing creatures to enable Ai to deploy her full power and purge the infection. Ultimately discharged from CURE alongside Ai, they move forward together beyond their military obligations. His character evolves from initial frustration and duty toward a protective stance regarding Ai, shaped by their shared experiences of confinement and mutual reliance.