Kyousuke Isazu heads Kiryu Hospital and acts as primary physician for Aiko Tachibana. His background includes artificial life form research at Kiryu Biotech alongside Susumu Kurose and Akiko Nanbara, where he developed "Carbon Nanostructure" technology. His life revolves around his daughter Yuzuha, who fell into a coma after an accident. Unable to cure her conventionally, he dedicated his research to finding a treatment. This drive becomes central to his later actions. During the mission to eradicate the "Burst" Malignant Matter outbreak, Isazu discovers thoughtless clones of Yuzuha within the original research facility. Using a neural interface device, he connects to these clones through Yuzuha's brain to control them remotely. He exploits this connection to manipulate Aiko Tachibana into returning from quarantine, intending to use her unique link to the Malignant Matter in experiments to revive his daughter. His psychological state deteriorates significantly. After linking to the clones, he suffers a severe mental breakdown, descending into irrational obsession. Even when Yuya Kanzaki reveals that Isazu's own actions prolong Yuzuha's coma, Isazu cannot process this truth, worsening his instability. Following the Burst incident's resolution, Isazu suffers severe mental trauma from his direct control of the Malignant Matter. He enters a recovery phase under the care of his daughter Yuzuha and a nurse named Saho.