Kyosuke Isazu directed Kiryu Hospital and acted as the primary physician for Aiko Tachibana. His background lay in artificial life form research at the Kiryu Biotech Research Facility, specializing in "Carbon Nanostructure" technology development. He collaborated closely with fellow researchers Susumu Kurose and Akiko Nanbara, college-era colleagues where Nanbara was one year their senior. The coma of his only daughter, Yuzuha Isazu, following an accident, became a profound personal motivation. His struggle to find effective treatments for her deeply influenced his decisions. This tragedy drove his involvement in research culminating in the catastrophic 2035 "Burst" incident within Kurobe Gorge, where artificial "Matter" life forms spiraled out of control. During the Burst, his experimental efforts to manipulate Malignant Matter aimed to heal Yuzuha, demanding significant ethical compromise. His single-minded pursuit led to high-risk decisions endangering others, reflecting a "mad scientist" archetype. Controlling the Malignant Matter inflicted severe mental trauma, particularly after the Burst's eradication. Following the incident's resolution, he entered a recovery period, cared for by Saho and his daughter Yuzuha. This marked a shift from antagonist to a figure focused on healing and reconciliation. The etymology of his name reflects aspects of his character: "Kyōsuke" combines "respectful, polite" (恭) and "forerunner, herald" (介), while "Isazu" incorporates "that one" (伊), "help, aid" (佐), and "haven, port, harbor, ferry" (津).